Leukocyte Series PDF 2024

PAGE 1 UNIVERSITÄTSMEDIZIN NEUMARKT A. M. https://edu.umch.de www.umfst.ro CAMPUS HAMBURG 2024 May The leukocytes Leukocytes (White Blood Cells)...

PAGE 1 UNIVERSITÄTSMEDIZIN NEUMARKT A. M. https://edu.umch.de www.umfst.ro CAMPUS HAMBURG 2024 May The leukocytes Leukocytes (White Blood Cells) PAGE 2 Definition: The leukocytes, also called white blood cells, are the mobile units of the body’s protective system. They are formed: partially in the bone marrow (granulocytes and monocytes and a few lymphocytes) partially in the lymph tissue (lymphocytes and plasma cells). After formation, they are transported in the blood to different parts of the body where they are needed. Leukocytes (White Blood Cells) PAGE 3 Six types of WBCs are normally present in the blood: – Granulocytes or, in clinical terminology, “polys”, because of the multiple nuclei: Polymorphonuclear neutrophils Polymorphonuclear eosinophils Polymorphonuclear basophils – Mononuclear cells: Monocytes Lymphocytes Plasma cells (occasionally) Types of White Blood Cells PAGE 4 1 2 3 1.Neutrophil 2.Eosinophil 3.Basophil 4.Monocyte 5.Lymphocite 6.Plasma cell 4 5 6 Prof dr Anca Bacârea, Personal collection Leukocytes (White Blood Cells) PAGE 5 The adult human being has about 7000 WBCs/µL of blood (4000-8000 WBC) (in comparison with 5 million red blood cells /µL of blood). Of the total WBCs, the normal percentages of the different types are approximately the following: Polymorphonuclear neutrophils 62.0% Polymorphonuclear eosinophils 2.3% Polymorphonuclear basophils 0.4% Monocytes 5.3% Lymphocytes 30.0% Genesis of white blood cells PAGE 6 Two major lineages of WBCs are formed: the myelocytic lineage, beginning with the myeloblast; the lymphocytic lineage, beginning with the lymphoblast. Guyton and Hall, Textbook of Medical Physiology, 2016 Genesis of white blood cells PAGE 7 The different cells of the myelocyte series are: 1, myeloblast; 2, promyelocyte; 3, megakaryocyte; 4, neutrophil myelocyte; 5, young neutrophil metamyelocyte; 6, “band” neutrophil metamyelocyte; 7, polymorphonuclear neutrophil; 8, eosinophil myelocyte; 9, eosinophil metamyelocyte; 10, polymorphonuclear eosinophil; 11, basophil myelocyte; 12, polymorphonuclear basophil; Guyton and Hall, Textbook of Medical Physiology, 2016 13-16, stages of monocyte formation. Genesis of white blood cells PAGE 8 CMP: common myeloid progenitors GMP: the granulocyte-monocyte progenitor CSF: colony-stimulating factor G-CSF: granulocyte colony-stimulating factor GM-CSF: granulocyte-macrophage colony-stimulating factor Rodak's Hematology, Fifth Ed., 2016 Genesis of white blood cells PAGE 9 The granulocytes and monocytes are formed only in the bone marrow. Lymphocytes and plasma cells are produced mainly in the various lymphogenous tissues- especially the lymph glands, spleen, thymus, tonsils, and various pockets of lymphoid tissue elsewhere in the body, such as in the bone marrow and in so-called Peyer’s patches underneath the epithelium in the gut wall. The lymphocytes are mostly stored in the various lymphoid tissues, except for a small number that are temporarily being transported in the blood. The WBCs formed in the bone marrow are stored within the marrow until they are needed in the circulatory system. Then, when the need arises, various factors cause them to be released. Normally, about three times as many WBCs are stored in the marrow as circulate in the entire blood. This quantity represents about a 6-day supply of these cells. Life span of white blood cells PAGE 10 The life of the granulocytes after being released from the bone marrow is normally 4 to 8 hours circulating in the blood and another 4 to 5 days in tissues where they are needed. – In times of serious tissue infection, this total life span is often shortened to only a few hours because the granulocytes proceed even more rapidly to the infected area, perform their functions and, in the process, are themselves destroyed. The monocytes also have a short transit time, 10 to 20 hours in the blood, before passing through the capillary membranes into the tissues. Once in the tissues, they swell to much larger sizes to become tissue macrophages, and, in this form, they can live for months unless destroyed while performing phagocytic functions. – The tissue macrophages are the basis of the tissue macrophage system, which provides continuing defense against infection. Life span of white blood cells PAGE 11 Lymphocytes enter the circulatory system continually, along with drainage of lymph from the lymph nodes and other lymphoid tissue. After a few hours, they pass out of the blood back into the tissues by diapedesis. Then they re-enter the lymph and return to the blood again and again; thus, there is continual circulation of lymphocytes through the body. The lymphocytes have life spans of weeks or months, depending on the body’s need for these cells.  PAGE 12 Neutrophils and macrophages defend against infections It is mainly the neutrophils and tissue macrophages that attack and destroy invading bacteria, viruses, and other injurious agents. 1. The neutrophils: are mature cells that can attack and destroy bacteria even in the circulating blood. 2. The tissue macrophages: begin life as blood monocytes, which are immature cells while still in the blood and have little ability to fight infectious agents at that time. Once they enter the tissues, they begin to swell-sometimes increasing their diameters as much as fivefold—to as great as 60 to 80 micrometers. These cells are now called macrophages, and they are extremely capable of combating disease agents in the tissues. Diapedesis PAGE 13 Neutrophils and monocytes can squeeze through the pores of the blood capillaries by diapedesis. Even though a pore is much smaller than a cell, a small portion of the cell slides through the pore at a time; the portion sliding through is momentarily constricted to the size of the pore. Guyton and Hall, Textbook of Medical Physiology, 2016 Diapedesis PAGE 14 Integrins and selectins (adhesion molecules) are of significant importance in allowing neutrophils to marginate as well as exit the blood and enter the tissues by diapedesis. Those neutrophils that do not migrate into the tissues eventually undergo programmed cell death or apoptosis and are removed by macrophages in the spleen. Once neutrophils are in the tissues, their life span is variable, depending on whether or not they are responding to infectious or inflammatory agents. Some products of inflammation and infection tend to prolong the neutrophil’s life span through anti-apoptotic signals. Neutrophil granules PAGE 15 Primary (Azurophilic) Granules - formed Secondary (Specific) Granules - formed during the promyelocyte stage and last to during myelocyte and metamyelocyte be released (exocytosis) contain: stages and third to be released contain: – Myeloperoxidase – b2-Microglobulin – Acid b-glycerophosphatase – Collagenase – Cathepsins – Gelatinase – Defensins – Lactoferrin – Elastase – Neutrophil gelatinase-associated – Proteinase-3 lipocalin – Others – Transcobalamin I – Others Neutrophil granules PAGE 16 Tertiary granules - formed during Secretory granules (secretory vesicles) - metamyelocyte and band stages and formed during band and segmented second to be released contain: neutrophil stages and first to be released – Gelatinase (fuse to plasma membrane) contain – Collagenase (attached to membrane): – Lysozyme – Integrins – Acetyltransferase – Alkaline phosphatase – b2-Microglobulin – Complement receptor Diapedesis PAGE 17 Neutrophil recruitment to an inflammatory site begins when chemotactic agents bind to neutrophil receptors. The first neutrophil response is to roll along endothelial cells of the blood vessels using stronger adhesive molecules than those used by nonstimulated marginated neutrophils. Rolling consists of transient adhesive contacts between neutrophil selectins and adhesive molecules on the surface of endothelial cells. At the same time, secretory granules containing additional adhesive molecules are fused to the neutrophil’s plasma membrane. Diapedesis PAGE 18 Integrins from secretory granules contribute to tight stationary binding between neutrophils and endothelial cells. This is followed by diapedesis or transmigration of neutrophils between endothelial cells—a process that is also mediated by integrins and integrin-associated proteins. Tertiary granules containing gelatinase and collagenase are released by transmigrating neutrophils. Gelatinase degrades denatured collagen as well as types IV and V collagen and activates chemokines. Neutrophils then migrate in a directional manner toward the area of greatest concentration of chemotactic agents. Chemotaxis PAGE 19 Many different chemical substances in the tissues cause both neutrophils and macrophages to move toward the source of the chemical. This phenomenon is known as chemotaxis. When a tissue becomes inflamed at least a dozen different products that can cause chemotaxis toward the inflamed area are formed: (1) some of the bacterial or viral toxins (2) degenerative products of the inflamed tissues (3) several reaction products of the “complement complex” activated in inflamed tissues (4) several reaction products caused by plasma clotting in the inflamed area (5) other substances. Chemotaxis PAGE 20 Chemotaxis depends on the concentration gradient of the chemotactic substance. The concentration is greatest near the source, which directs the unidirectional movement of the WBCs. Chemotaxis is effective up to 100 micrometers away from an inflamed tissue. Therefore, because almost no tissue area is more than 50 micrometers away from a capillary, the chemotactic signal can easily move WBCs from the capillaries into the inflamed area.  PAGE 21 Phagocytosis The most important function of the neutrophils and macrophages is phagocytosis, which means cellular ingestion of the offending agent. Phagocytes must be selective of the material that is phagocytized; otherwise, normal cells and structures of the body might be ingested. Whether phagocytosis will occur depends especially on three selective procedures: 1. Most natural structures in the tissues have smooth surfaces, which resist phagocytosis. If the surface is rough, the likelihood of phagocytosis is increased. 2. Most natural substances of the body have protective protein coats that repel the phagocytes. Conversely, most dead tissues and foreign particles have no protective coats, which makes them subject to phagocytosis.  PAGE 22 Phagocytosis 3. The immune system of the body develops antibodies against infectious agents such as bacteria. – The antibodies then adhere to the bacterial membranes and thereby make the bacteria especially susceptible to phagocytosis. – To do this, the antibody molecule also combines with the C3 product of the complement cascade. The C3 molecules, in turn, attach to receptors on the phagocyte membrane, thus initiating phagocytosis-> this process by which a pathogen is selected for phagocytosis and destruction is called opsonization. Phagocytosis- Opsonization PAGE 23 Phagocytosis by neutrophils PAGE 24 Recognition and Attachment Killing and Digestion – Phagocyte receptors recognize Oxygen Dependent and bind to certain foreign – Respiratory burst through the activation of NADPH oxidase. H2O2 and hypochlorite are produced. molecular patterns and Oxygen Independent opsonins such as antibodies and – The pH within the phagosome becomes alkaline complement components. and then neutral, the pH at which digestive Ingestion enzymes work. – Pseudopodia are extended – Primary and secondary lysosomes (granules) fuse to the phagosome and empty hydrolytic enzymes around the foreign particle and and other bactericidal molecules into the enclose it within a “phagosome” phagosome. (engulfment). Formation of Neutrophil Extracellular Traps – The phagosome is pulled – Nuclear and organelle membranes dissolve, and toward the center of the cell by activated cytoplasmic enzymes attach to DNA. polymerization of actin and – The cytoplasmic membrane ruptures, and DNA with attached enzymes is expelled so that the myosin and by microtubules. bacteria are digested in the external environment.  PAGE 25 Phagocytosis by neutrophils The neutrophils entering the tissues are already mature cells that can immediately begin phagocytosis. A single neutrophil can usually phagocytize 3 to 20 bacteria before the neutrophil becomes inactivated and dies. https://teachmephysiology.com/immune-system/innate-immune-system/phagocytosis/ Phagocytosis by macrophages PAGE 26 When activated by the immune system, they are much more powerful phagocytes than neutrophils, often capable of phagocytizing as many as 100 bacteria. They also have the ability to engulf much larger particles, even whole RBCs or, occasionally, malarial parasites, whereas neutrophils are not capable of phagocytizing particles much larger than bacteria. Also, after digesting particles, macrophages can extrude the residual products and often survive and function for many more months. Phagocytosis PAGE 27 Once a foreign particle has been phagocytized, lysosomes and other cytoplasmic granules in the neutrophil or macrophage immediately come in contact with the phagocytic vesicle, and their membranes fuse, thereby dumping many digestive enzymes and bactericidal agents into the vesicle. Thus, the phagocytic vesicle now becomes a digestive vesicle, and digestion of the phagocytized particle begins immediately. Both neutrophils and macrophages contain an abundance of lysosomes filled with proteolytic enzymes especially geared for digesting bacteria and other foreign protein matter. The lysosomes of macrophages (but not of neutrophils) also contain large amounts of lipases, which digest the thick lipid membranes possessed by some bacteria such as the tuberculosis bacillus. Phagocytosis PAGE 28 In addition to the digestion of ingested bacteria in phagosomes, neutrophils and macrophages contain bactericidal agents that kill most bacteria even when the lysosomal enzymes fail to digest them. This characteristic is especially important because some bacteria have protective coats or other factors that prevent their destruction by digestive enzymes. Much of the killing effect results from several powerful oxidizing agents formed by enzymes in the membrane of the phagosome or by a special organelle called the peroxisome. These oxidizing agents include large quantities of superoxide (O2−), hydrogen peroxide (H2O2), and hydroxyl ions (OH−), which are lethal to most bacteria, even in small quantities. Also, one of the lysosomal enzymes, myeloperoxidase, catalyzes the reaction between H2O2 and chloride ions to form hypochlorite, which is exceedingly bactericidal. Phagocytosis PAGE 29 Prof dr Anca Bacârea, Personal collection  PAGE 30 Monocyte-macrophage cell system (reticuloendothelial system) After entering the tissues and becoming macrophages, another large portion of monocytes becomes attached to the tissues and remains attached for months or even years until they are called on to perform specific local protective functions. They have the same capabilities as the mobile macrophages to phagocytize large quantities of bacteria, viruses, necrotic tissue, or other foreign particles in the tissue. When appropriately stimulated, they can break away from their attachments and once again become mobile macrophages that respond to chemotaxis and all the other stimuli related to the inflammatory process. Thus, the body has a widespread “monocyte-macrophage system” in virtually all tissue areas.  PAGE 31 Monocyte-macrophage cell system (reticuloendothelial system) The total combination of monocytes, mobile macrophages, fixed tissue macrophages, and a few specialized endothelial cells in the bone marrow, spleen, and lymph nodes is called the reticuloendothelial system. All or almost all these cells originate from monocytic stem cells; therefore, the reticuloendothelial system is almost synonymous with the monocyte-macrophage system. Because the term reticuloendothelial system is much better known in medical literature than the term monocyte-macrophage system, it should be remembered as a generalized phagocytic system located in all tissues, especially in the tissue areas where large quantities of particles, toxins, and other unwanted substances must be destroyed.  PAGE 32 Monocyte-macrophage cell system (reticuloendothelial system) 1. Tissue macrophages in the skin and subcutaneous tissues (histiocytes) Although the skin is mainly impregnable to infectious agents, this is no longer true when the skin is broken. When infection begins in a subcutaneous tissue and local inflammation ensues, local tissue macrophages can divide in situ and form still more macrophages. Then they perform the usual functions of attacking and destroying the infectious agents. Monocyte-macrophage cell system (reticuloendothelial PAGE 33 system) 2. Macrophages in the lymph nodes Essentially no particulate matter that enters the tissues, such as bacteria, can be absorbed directly through the capillary membranes into the blood. If the particles are not destroyed locally in the tissues, they enter the lymph and flow to the lymph nodes located intermittently along the course of the lymph flow. The foreign particles are then trapped in lymph nodes in a meshwork of sinuses lined by tissue macrophages. Guyton and Hall, Textbook of Medical Physiology, 2016 Monocyte-macrophage cell system (reticuloendothelial PAGE 34 system) 3. Alveolar macrophages in the lungs Another route by which invading organisms frequently enter the body is through the lungs. Large numbers of tissue macrophages are present as integral components of the alveolar walls. They can phagocytize particles that become entrapped in the alveoli. – If the particles are digestible, the macrophages can also digest them and release the digestive products into the lymph. – If the particle is not digestible, the macrophages often form a “giant cell” capsule around the particle until it can maybe be slowly dissolved. Such capsules are frequently formed around tuberculosis bacilli, silica dust particles, and even carbon particles. Monocyte-macrophage cell system (reticuloendothelial PAGE 35 system) 4. Macrophages (Kupffer cells) in the liver sinusoids Another route by which bacteria invade the body is through the gastrointestinal tract. Large numbers of bacteria from ingested food constantly pass through the gastrointestinal mucosa into the portal blood. Before this blood enters the general circulation, it passes through the liver sinusoids, which are lined with tissue macrophages called Kupffer cells. These cells form such an effective particulate filtration system that almost none of the bacteria from the gastrointestinal tract pass from the portal blood into the general systemic circulation. Motion pictures of phagocytosis by Kupffer cells have demonstrated phagocytosis of a single bacterium in less Guyton and Hall, Textbook of Medical Physiology, than 0.01 seconds. 2016 Monocyte-macrophage cell system (reticuloendothelial PAGE 36 system) 5. Macrophages of the spleen and bone marrow If an invading organism succeeds in entering the general circulation, there are other lines of defense by the tissue macrophage system, especially by macrophages of the spleen and bone marrow. In both these tissues, macrophages become entrapped by the reticular meshwork of the two organs and when foreign particles come in contact with these macrophages, they are phagocytized. The spleen is similar to the lymph nodes, except that blood, instead of lymph, flows through the tissue spaces of the spleen. Monocyte-macrophage cell system (reticuloendothelial PAGE 37 system) 5. Macrophages of the spleen and bone marrow A small artery penetrates from the splenic capsule into the splenic pulp and terminates in small capillaries. The capillaries are highly porous, allowing whole blood to pass out of the capillaries into cords of red pulp. The blood then gradually squeezes through the trabecular meshwork of these cords and eventually returns to the circulation through the endothelial walls of the venous sinuses. The trabeculae of the red pulp and the venous sinuses are lined with vast numbers of macrophages. This peculiar passage of blood through the cords of the red pulp provides an exceptional means of phagocytizing unwanted debris in the blood, including especially old and abnormal RBCs. Eosinophils PAGE 38 Eosinophils are weak phagocytes, and they exhibit chemotaxis, but in comparison with the neutrophils, it is doubtful that the eosinophils are significant in protecting against the usual types of infection. Eosinophils, are often produced in large numbers in people with parasitic infections, and they migrate into tissues diseased by parasites. Although most parasites are too large to be phagocytized by eosinophils or any other phagocytic cells, eosinophils attach themselves to the parasites by way of special surface molecules and release substances that kill many of the parasites. They do so in several ways: (1) by releasing hydrolytic enzymes from their granules, which are modified lysosomes (2) probably by also releasing highly reactive forms of oxygen that are especially lethal to parasites (3) by releasing from the granules a highly larvacidal polypeptide called major basic protein.  PAGE 39 Eosinophils Eosinophils also have a special propensity to collect in tissues in which allergic reactions occur, such as in the peribronchial tissues of the lungs in people with asthma and in the skin after allergic skin reactions. This action is caused at least partly by the fact that many mast cells and basophils participate in allergic reactions. The mast cells and basophils release an eosinophil chemotactic factor that causes eosinophils to migrate toward the inflamed allergic tissue. The eosinophils are believed to detoxify some of the inflammation-inducing substances released by the mast cells and basophils and probably also phagocytize and destroy allergen-antibody complexes, thus preventing excess spread of the local inflammatory process.  PAGE 40 Basophils The basophils in the circulating blood are similar to the large tissue mast cells located immediately outside many of the capillaries in the body. Both mast cells and basophils liberate heparin into the blood. – Heparin is a substance that can prevent blood coagulation. The mast cells and basophils also release small quantities of bradykinin and serotonin. It is mainly the mast cells in inflamed tissues that release these substances during inflammation.  PAGE 41 Basophils The mast cells and basophils play an important role in some types of allergic reactions because the type of antibody that causes allergic reactions, the immunoglobulin E (IgE) type, has a special propensity to become attached to mast cells and basophils. Then, when the specific antigen for the specific IgE antibody subsequently reacts with the antibody, the resulting attachment of antigen to antibody causes the mast cell or basophil to rupture and release large quantities of histamine, bradykinin, serotonin, heparin, slow- reacting substance of anaphylaxis (a mixture of three leukotrienes), and a number of lysosomal enzymes. These substances cause local vascular and tissue reactions that cause many, if not most, of the allergic manifestations. Lymphocytes PAGE 42 Lymphocytes are responsible for immunity. The lymphocytes are located most extensively in the lymph nodes, but they are also found in special lymphoid tissues such as the spleen, submucosal areas of the gastrointestinal tract, thymus, and bone marrow. The lymphoid tissue is distributed advantageously in the body to intercept invading organisms or toxins before they can spread too widely. The invading agent first enters the tissue fluids and then is carried by lymph vessels to the lymph node or other lymphoid tissue. Three categories: – T Lymphocytes – B Lymphocytes – NK Lymphocytes Lymphocytes PAGE 43 T and B lymphocytes promote “cell-mediated” immunity or “humoral” immunity. Both types of lymphocytes are derived from pluripotent hematopoietic stem cells that form common lymphoid progenitor cells: 1. The lymphoid progenitor cells that are destined to form activated T lymphocytes first migrate and are preprocessed in the thymus gland, and thus they are called “T” lymphocytes to designate the role of the thymus. They are responsible for cell-mediated immunity. 2. The B lymphocytes are destined to form antibodies—are preprocessed in the liver during mid- fetal life and in the bone marrow in late fetal life and after birth. This population of cells was first discovered in birds, which have a special preprocessing organ called the bursa of Fabricius. For this reason, these lymphocytes are called “B” lymphocytes to designate the role of the bursa, and they are responsible for humoral immunity. Lymphocytes PAGE 44 Guyton and Hall, Textbook of Medical Physiology, 2016 Lymphocytes PAGE 45 The T lymphocytes, after origination in the bone marrow, first migrate to the thymus gland. Here they divide rapidly and at the same time develop extreme diversity for reacting against different specific antigens. – The thymic lymphocyte develops specific reactivity against one antigen, and then the next lymphocyte develops specificity against another antigen. This process continues until there are thousands of different types of thymic lymphocytes with specific reactivities against many thousands of different antigens. – These different types of preprocessed T lymphocytes now leave the thymus and spread by way of the blood throughout the body to lodge in lymphoid tissue everywhere. Lymphocytes PAGE 46 The thymus also makes certain that any T lymphocytes leaving the thymus will not react against proteins or other antigens that are present in the body’s own tissues. The thymus selects which T lymphocytes will be released by first mixing them with virtually all the specific “self-antigens” from the body’s own tissues. !!! If a T lymphocyte reacts, it is destroyed and phagocytized instead of being released, which happens to up to 90% of the cells. Before leaving the thymus they gain the T cell receptor, necessary for their immune function. Lymphocytes PAGE 47 Thymus-derived T lymphocytes develop into the effector cells of cellular immunity and “help” B cells to produce antibodies against protein antigens. T cells constitute 60% to 70% of the lymphocytes in peripheral blood and are the major lymphocyte population in splenic periarteriolar sheaths and lymph node interfollicular zones. T cells cannot recognize free or circulating antigens; instead, the vast majority (>95%) of T cells sense only peptide fragments of proteins displayed by molecules of the major histocompatibility complex (MHC). Because T cell antigen receptors have evolved to see MHC-bound peptides on cell surfaces, T cells only recognize antigens presented by other cells. The outcome of this interaction varies, depending on the type of T cell that is involved and the identity of the other interacting cell, ranging from the killing of virus-infected cells to the activation of phagocytes or B lymphocytes that have ingested protein antigens. Lymphocytes PAGE 48 Peptide antigens presented by MHC molecules are recognized by the T-cell receptor (TCR), a heterodimer that in most T cells is composed of disulfide-linked α and β protein chains. Each chain has a variable region that participates in binding a particular peptide antigen and a constant region that interacts with associated signaling molecules. TCRs are noncovalently linked to a cluster of five invariant polypeptide chains: the γ (gamma), δ (delta), and ε (epsilon) proteins of the CD3 molecular complex and two ζ (zetta) chains. The CD3 proteins and ζ chains do not bind antigens; instead, they are attached to the TCR and initiate intracellular biochemical signals after TCR recognition of antigen. T Lymphocytes PAGE 49 They are classified into three major groups and the functions of each of these T cells are distinct: (1) helper T cells (2) cytotoxic T cells (3) suppressor T cells T Helper Lymphocytes PAGE 50 T-helper cells are the most numerous of the T cells and usually represent more than three quarters of T cells. They serve as the major regulator of virtually all immune functions. Some helper T cells help B cells produce antibodies against foreign antigens. Others help activate killer T cells to kill foreign or abnormal cells or help activate macrophages enabling them to ingest foreign or abnormal cells more efficiently. They do this by forming a series of protein mediators, called lymphokines, that act on other cells of the immune system, as well as on bone marrow cells. Among the most important lymphokines secreted by the T-helper cells are the following: interleukin-2, interleukin-3, interleukin-4, interleukin-5, interleukin-6, granulocyte-monocyte colony-stimulating factor, interferon-γ. T helper Lymphocytes PAGE 51 T helper lymphocytes have subpopulations like TH1 and TH2 - a key role in regulating the inflammatory response. – E.g. In the pathogenesis of sepsis, the acquired immune response will be transformed from a TH1 mediated immune response into a cell TH2 mediated immune response. – It initiates the production and biphasic release of cytokines with antagonistic action. The Th1 response: is characterized by the production of interferon - gamma, which activates the bactericidal activities of macrophages, and induces B-cells to make opsonizing (coating) antibodies, and leads to cell mediated immunity. The Th2 response: is characterized by the release of interleukin 4, which results in the activation of B-cells to make neutralizing (killing) antibodies, leading to humoral immunity. Generally, Th1 responses are more effective against intracellular pathogens (viruses and bacteria that are inside host cells), while Th2 responses are more effective against extracellular bacteria, parasites and toxins. T Lymphocytes PAGE 52 Killer (cytotoxic) T cells (CD8) attach to particular foreign or abnormal (for example infected) cells because they have encountered them before. Killer T cells may kill these cells by making holes in their cell membrane and injecting enzymes into the cells or by binding with certain sites on their surface called death receptors. Suppressor (regulatory) T cells produce substances that help end the immune response or sometimes prevent certain harmful responses from occurring. Sometimes T cells-for reasons that are not completely understood - do not distinguish self from nonself. This malfunction can result in an autoimmune disorder, in which the body attacks its own tissues. T Lymphocytes PAGE 53 γδ T cells (gamma delta T cells) represent a small subset of T cells, which possess a different receptor on the surface (TCR). Most T cells receptor consists of two chains α-and β-gp. Unlike T cells, γδ cells have a TCR composed of gamma and a delta chains. This group is more poorly represented than beta alpha cells. They are abundant in the intestinal mucosa. Natural killer T cells (NKT) are a heterogeneous group of T cells, which have properties of both NK cells and T cells and represents only 0.2% of all circulating T lymphocytes in the blood. NK Lymphocytes PAGE 54 NK lymphocytes- similar from the morphological point of view but different as a function. NK cells are capable of spontaneously destroying tumoral cells or viral infected cells and they represent approximately 15% from the lymphocytes found in the peripheral blood. NK cells are formed from common progenitor cells with T and B lymphocytes but they belong to the innate immunity!!! B Lymphocytes PAGE 55 B lymphocytes are derived from the bone marrow (BM), representing 10-20% of circulating lymphocytes. They are found in the BM and lymphoid follicles in peripheral lymphoid tissues: lymph nodes, spleen, tonsils, mucosa associated lymphoid tissue (MALT). It has on its surface a specific receptor: BCR (B cell receptor). They recognize different chemical structures: soluble proteins, cell-associated proteins, lipids, polysaccharides, nucleic acids. B Lymphocytes PAGE 56 B lymphocytes are different from T lymphocytes in two ways: – First, instead of the whole cell developing reactivity against the antigen, as occurs for the T lymphocytes, the B lymphocytes actively secrete antibodies that are the reactive agents. These agents are large proteins that are capable of combining with and destroying the antigenic substance. – Second, the B lymphocytes have even greater diversity than the T lymphocytes, thus forming many millions of types of B-lymphocyte antibodies with different specific reactivities. After preprocessing, the B lymphocytes, like the T lymphocytes, migrate to lymphoid tissue throughout the body, where they lodge near but slightly removed from the T-lymphocyte areas. Plasma cells PAGE 57 B lymphocytes are transformed into plasmocytes that synthesize large amounts of antibodies – immunoglobulins. There are 5 antibody isotypes: IgA, IgD, IgE, IgG, IgM, each of which has a role in complement activation and recruitment of inflammatory cells: – IgG and IgM = 95% of circulating antibodies – IgA in mucous membranes – IgD is not secreted, but is on the surface of B lymphocytes – IgE is found in small amounts in circulation and binds to tissue mast cells being involved in triggering the anaphylactic reactions.  PAGE 58 White blood cells’ disorders White blood cells’ disorders PAGE 59 Classification: I. NON-MALIGNANT disorders of the WBC: A. Quantitative disorders= increase/decrease of the cells’ number 1. Leukocytosis = ↑ cells’ number 2. Leukopenia = ↓ cells’ number B. Qualitative disorders= modification of a cell’s function II. MALIGNANT disorders : A. Acute or chronic leukemias B. Hodgkin or non-Hodgkin lymphoma C. Lymphoplasmacytic neoplasia Leukocytosis PAGE 60 Leukocytosis occurs as a response towards different stress factors: – Infections – Sustained physical effort or psychological stress – Temperature modifications – General anesthesia, surgery, pregnancy – Some drugs, toxins – Excess hormones – Cancer – Hematological disorders Leukocytosis PAGE 61 The increase of granulocytes (neutrophils, eosinophils and basophiles) and monocytes it occurs mostly as a response towards infections. – Granulocytosis – increase of the number of all types of granulocytes: neutrophils, eosinophils, basophils. – Neutrophilia refers to an almost exclusive increase of neutrophils. Other causes can be found within the bone marrow – in case of increased production in lymphoproliferative disorders: polycythemia vera, acute or chronic leukemia. Leukocytosis PAGE 62 Neutrophilia – When the neutrophils’ peripheral request and release from the bone marrow it is increased, deposits are mobilized and medullary production it is activated. – Production it is accelerated and, as a result, immature cells are going to be released in the peripheral circulation. – The release of immature leukocytes in the peripheral blood it is called a “leukemoid reaction” or a “left shift of the leukocytes’ formula”. – After the initial cause (infection) has been resolved, the leukocytes’ formula gets back to normal. Leukocytosis PAGE 63 Neutrophilia- causes: – Physiological: In newborns Pregnancy In labor Post-partum After exercise – Drugs or toxics: Administration of corticosteroids - may increase the release of neutrophils from the bone marrow and reduce their migration into tissues; Acute poisoning with Pb, Hg, some venoms; – Reactive neutrophilia - the result of increased release of neutrophils from BM to compensate their high affinity for tissues. It is frequently accompanied by deviation to the left of the leukocyte formula (leukemoid reaction); – Metabolic and endocrine diseases: e.g. diabetic ketoacidosis, acute renal failure, acute gout crises – Some malignant hematologic diseases. Leukocytosis PAGE 64 Eosinophilia Definition: increase of the absolute number of eosinophils in the peripheral blood of over 450 cells/mm3. Causes: – Allergic diseases: asthma, allergic rhinitis, eczema, atopic dermatitis – Parasitic infections – Fungal and other infections – Tuberculosis – Hematologic malignancies and nonhematologic (lung, vaginal, skin, stomach carcinoma, malignant melanoma) – Drugs: aspirin, beta blockers, penicillin, cephalosporins, NSAIDs, etc. – Idiopathic - is diagnosis of exclusion. Leukocytosis PAGE 65 Monocytosis Definition: increase of the monocytes’ number over 800 cells/mm3. Causes: It is usually transient and it does not necessarily correlates with a dysfunction of monocytes. It can occur in bacterial infections: o especially in the healing phase, when the phagocytic capacity increases or after a neutropenia/ agranulocytosis. o chronic infections in which bacteria are intracellular: tuberculosis, brucellosis, listeriosis. In newborns it is physiological. Leukocytosis PAGE 66 Lymphocytosis Definition: increase of the lymphocytes’ number. Causes: It occurs in case of antigenic stimulation. It rarely occurs in acute bacterial infections. It is commonly seen in chronic bacterial infections: congenital syphilis or tertiary syphilis. It is also very common in case of acute viral infections: EBV, CMV, herpes, viral hepatitis. Endocrine causes: thyrotoxicosis, adrenal insufficiency. Leukocytosis PAGE 67 Lymphocytosis Causes of absolute lymphocytosis include: – Acute viral infections, such as infectious mononucleosis (glandular fever), hepatitis and cytomegalovirus infection – Other acute infections such as pertussis – Protozoal infections, such as toxoplasmosis – Chronic intracellular bacterial infections such as tuberculosis or brucellosis – Chronic lymphocytic leukemia. Causes of relative lymphocytosis include: – Age less than 2 years – Connective tissue diseases – Splenomegaly with splenic sequestration of granulocytes – Exercise – Stress. Leukopenia PAGE 68 Leukopenia - the bone marrow produces very few WBCs. This condition leaves the body unprotected against many bacteria and other agents that might invade the tissues. Normally, the human body lives in symbiosis with many bacteria because all the mucous membranes of the body are constantly exposed to large numbers of bacteria. – The mouth almost always contains various spirochetal, pneumococcal, and streptococcal bacteria, and these same bacteria are present to a lesser extent in the entire respiratory tract. – The distal gastrointestinal tract is especially loaded with colon bacilli. – We always find bacteria on the surfaces of the eyes, urethra, and vagina. Any decrease in the number of WBCs immediately allows invasion of adjacent tissues by bacteria that are already present. Leukopenia PAGE 69 Within 2 days after the bone marrow stops producing WBCs, ulcers may appear in the mouth and colon, or some form of severe respiratory infection might develop. Bacteria from the ulcers rapidly invade surrounding tissues and the blood. Without treatment, death often ensues in less than a week after acute total leukopenia begins!!! Leukopenia is pathological! It is defined as a decrease of the WBC’s absolute number below 4000/mm3. Leukopenia PAGE 70 Irradiation of the body by x-rays or gamma rays, or exposure to drugs and chemicals that contain benzene or anthracene nuclei, is likely to cause aplasia of the bone marrow. Some common drugs such as chloramphenicol (an antibiotic), thiouracil (used to treat thyrotoxicosis), and even various barbiturate hypnotics on rare occasions cause leukopenia. After moderate irradiation injury to the bone marrow, some stem cells, myeloblasts, and hemocytoblasts may remain undestroyed in the marrow and are capable of regenerating the bone marrow, provided sufficient time is available. A patient properly treated with transfusions, plus antibiotics and other drugs to ward off infection, usually develops enough new bone marrow within weeks to months for blood cell concentrations to return to normal. Leukopenia PAGE 71 Neutropenia: refers specifically to a decrease in neutrophils. It commonly is defined as a circulating neutrophil count (absolute neutrophils count, ANC) of less than 1500 cells/μL. – ANC – mild decrease = 1000 – 1500 cells/mm3 – ANC – moderate decrease= 500 – 1000 cells/mm3 – ANC – severe decrease= < 500 cells/mm3 When ANC is below 500 neutrophils there is a great risk for severe infections that can endanger the patient’s life. Agranulocytosis, which denotes a severe neutropenia, is characterized by a circulating neutrophil count of less than 200 cells/μL. Leukopenia PAGE 72 Neutropenia: Causes: – X rays – Anaphylactic shock – Autoimmune disorders – Immune deficiencies – Exposure to different drugs or chemical substances Leukopenia PAGE 73 Neutropenia can be: 1. Acquired Accelerated removal - removal of neutrophils from the circulation exceeds production – Inflammation – Infection, viral or bacterial Increased destruction Alcoholism Carentiale states: e.g. folic acid, vitamin B12, iron Aplastic anemia - all of the myeloid stem cells are affected, resulting in anemia, thrombocytopenia, and agranulocytosis; Leukopenia PAGE 74 Neutropenia can be: 2. Congenital Kostmann’s syndrome – It occurs sporadically as an autosomal recessive disorder, causes severe neutropenia while preserving the erythroid and megakaryocyte cell lineages that result in red blood cell and platelet production. – The total white blood cell count may be within normal limits, but the neutrophil count is less than 200/μL. Monocyte and eosinophil levels may be elevated (compensatory). Leukopenia PAGE 75 Eosinopenia – decrease of the eosinophils’ number in the peripheral blood. Causes: It usually occurs due to eosinophilic migration towards inflammatory sites in the organism. Other causes can be Cushing syndrome, surgical stress, trauma, burns, shock, psychological stress. Leukopenia PAGE 76 Monocytopenia – decrease of the monocytes’ number. Rare and hard to diagnose because normally the monocytes’ number in the peripheral blood it is very low. It can be associated with a chronic treatment with glucocorticoids. Leukopenia PAGE 77 Lymphopenia – decrease of the lymphocytes’ number. Occurs in case of: – Abnormal production as in neoplasia: acute or chronic leukemia, non-hematological malignancies – Immune deficiencies, agammaglobulinemia – Marked destruction in viral infections, exposure to drugs or radiations – Congestive heart failure, renal failure – HIV/AIDS – Lymphopenia with an excessive decrease of Th cells  PAGE 78 References Guyton and Hall, Textbook of Medical Physiology, 2016 Rodak's Hematology, fifth edition, 2016