Lecture 3

• The conjunctiva was hyperemic, swollen, and purulent.

Lecture 3: Objectives

• Describe the overview of inflammation and its general features.
• Correlate the cardinal signs of inflammation with pathophysiologic events that characterize acute inflammation.
• Distinguish between the inflammatory cells of acute and chronic Inflammation.
• Describe the causes of inflammation and recognition of microbes and damaged cells.
• Describe the reaction of blood vessels in acute inflammation, including vascular flow & caliber changes, vascular leakage, responses of lymphatics & edema.
• Briefly describe leukocyte recruitment at site of inflammation- adhesion, migration, and chemotaxis
• Distinguish between exudate vs transudate for interstitial fluids
• Describe phagocytosis recognition, engulfment and intracellular destruction of microbes, debris (Reactive Oxygen Species, Nitric Oxide, Enzymes and Neutrophil Extracellular Traps) and the role of the complement system.
• Describe the leukocyte-mediated tissue injury and the termination of the acute inflammatory response.

Inflammation: Definitions and Clinical Features

• Inflammation is a systemic and local reaction of tissues and microcirculation to a pathogenic insult.
• Inflammation allows inflammatory cells, plasma proteins, and fluid to exit blood vessels and enter the interstitial space.
• Inflammation is divided into acute and chronic types.

Acute Inflammation

• Occurs in response to infections to eliminate pathogens, or in tissue necrosis to clear necrotic debris.
• Acute inflammation involves edema and neutrophils in tissues.

Acute Inflammation: Cardinal Signs

• Redness (rubor) and warmth (calor) are caused by vasodilation, which increases blood flow, occurring via relaxation of arteriolar smooth muscle.
• Key mediators of redness/warmth are histamine, prostaglandins, and bradykinin.
• Swelling (tumor) occurs due to leakage of fluid from postcapillary venules into the interstitial space, forming exudate.
• Key mediators of swelling include histamine, which causes endothelial cell contraction.
• Tissue damage leads to endothelial cell disruption.
• Edema results from increased blood flow to the injured area and increased vascular permeability, leading to the accumulation of extravascular fluid rich in plasma proteins.
• Pain (dolor) involves the releasing of prostaglandins, neuropeptides, and cytokines.
• Bradykinin and PGE2 sensitize sensory nerve endings, contributing to pain.
• Loss of function (functio laesa) occurs when leukocytes, recruited and activated by the offending agent and by endogenous mediators, release toxic metabolites and proteases extracellularly.
• Fever is caused by pyrogens (e.g., LPS from bacteria) that cause macrophages to release IL-1, IL-6, and TNF, which increase cyclooxygenase activity in perivascular cells of the hypothalamus.

Outcomes of Acute Inflammation

• Resolution and healing can occur via anti-inflammatory cytokines like IL-10 and TGF-B.
• Continued acute inflammation leads to persistent pus formation.
• IL-8 from macrophages recruits additional neutrophils.
• Abscess formation involves acute inflammation surrounded by fibrosis.
• Macrophages mediate fibrosis via fibrogenic growth factors and cytokines.
• Chronic inflammation occurs when macrophages present antigens to activate CD4+ helper T cells, which secrete cytokines that promote inflammation.

Cells of Acute Inflammation: Morphology and Function

• Neutrophils are the most prominent inflammatory cells in foci of acute inflammation during the first 24 hours.
• Neutrophilia is an increased count of neutrophils in the peripheral blood.
• Common etiologies for neutrophilia include bacterial infections and infarction.
• Normal neutrophils show nuclear segmentation and normal granulation of the cytoplasm.
• Neutrophils typically have 3-5 nuclear lobes with a thin strand of chromatin connecting these lobes.
• The cytoplasm of a neutrophil has a pinkish tint coming from secondary granules.
• Neutrophilia is commonly seen in persons presenting with acute bacterial, some viral, and rare fungal infections.
• Neutrophilia indicates densely packed polymorphonuclear leukocytes (PMNs) with multilobed nuclei

Chronic Inflammation: Definition

• Chronic inflammation is an outcome of acute inflammation, when the inciting injury is persistent or recurrent.
• Inflammation occurs when the inflammatory reaction is insufficient to completely degrade the agent.
• Inflammation involves, delayed response, but more specific (adaptive immunity) than acute inflammation.
• Lymphocytes and plasma cells are the main cells involved.

Cells of Chronic Inflammation: Morphology and Function

• Lymphocytes are the most prominent inflammatory cells in many viral infections.
• Monocytes/macrophages and plasma cells are also the most prominent cells in chronic inflammation.
• Lymphocytosis increases the number of lymphocytes in the peripheral blood.
• The peripheral blood smear from a normal adult female shows uniform erythrocytes with a normal central pallor, normal platelets, and a nonactivated lymphocyte.
• There is some variation in platelet size (black curved arrow), but all platelets are well-granulated
• Lymphocytes may be seen in a variety of viral infections.
• Infectious mononucleosis must be considered in a young person with lymphocytosis and marked lymphocyte heterogeneity
• Monocytes-macrophages replace neutrophils after 2-3 days; engulf larger particles, are longer lived, and can divide/proliferate within the inflamed tissue.
• Monocytosis increases the number of monocytes in the peripheral blood.
• A monocyte is characterized by a large size, blue-gray cytoplasm with occasional granules and vacuoles, and a somewhat folded nucleus.
• The lymphocytes (double-headed arrow), plasma cells (arrows) and a few macrophages (arrowheads) are present
• Eosinophils are predominant inflammatory cells in allergic reactions and parasitic infestations.
• Mast cells and basophils are sources of histamine.
• Important causes of basophilia include chronic myelogenous leukemia and other myeloproliferative diseases.
• Review Question #1: A 72 year-old male presents with productive cough, fever, chills and signs of toxicity, plus consolidation and rales over the right lung base. Sputum culture is positive for Streptococcus pneumoniae. There is an intra-alveolar exudate filling the alveoli. Neutrophils are the most likely type of inflammatory cell here.
• Review Question #2: 22 year-old medical student reports of frequent sneezing and watery eyes during the spring and summer. An increased number of eosinophils is more likely due to the described symptoms.

Causes of Inflammation

• Neutrophilic leukocytosis is caused by acute bacterial infections, especially by pyogenic organisms.
• Neutrophilic leukocytosis is caused by sterile inflammation, such as tissue necrosis (myocardial infarction, burns).
• Eosinophilic leukocytosis (eosinophilia) occurs in allergic disorders like asthma, hay fever, and parasitic infestations.
• Eosinophilic leukocytosis (eosinophilia) occurs in drug reactions as well as certain malignancies (e.g., Hodgkin and some non-Hodgkin lymphomas).
• autoimmune disorders (e.g., pemphigus, dermatitis herpetiformis) and some vasculitides cause eosinophilic leukocytosis (eosinophilia)
• Atheroembolic disease (transient) can eosinophilic leukocytosis (eosinophilia)
• Basophilic leukocytosis (basophilia) is rare, but may indicates myeloproliferative neoplasm (e.g., chronic myeloid leukemia).
• Monocytosis is caused by chronic infections (e.g., tuberculosis), bacterial endocarditis, rickettsiosis, and malaria.
• Monocytosis is caused by autoimmune disorders (e.g., systemic lupus erythematosus) and inflammatory bowel diseases (e.g., ulcerative colitis).
• Lymphocytosis accompanies monocytosis in many chronic immunologic stimulation disorders such as tuberculosis, brucellosis, or cytomegalovirus, or bacterial infections pertussis.

Reaction of Blood Vessels in Acute Inflammation

• Vascular reactions involve changes in the flow of blood and the permeability of vessels.
• Blood flow changes to movement of plasma protein and leukocytes to the injury site.
• Exudation is escape of fluid, proteins, and blood cells from the vascular system into the interstitial tissue or body cavities.
• Exudate is extravascular fluid that has a high protein concentration and contains cellular debris.
• Exudate implies the existence of an inflammatory process that has increased the permeability of small blood vessels.
• Transudate is fluid with protein content (mostly albumin), little or no cellular material, and low specific gravity.
• Occurs as an ultrafiltrate of blood plasma that is produced as a result of osmotic or hydrostatic imbalance without increase in vascular permeability.
• Edema defined as excess of fluid in the interstitial tissue or serous cavities, can be an exudate or a transudate.
• Pus is a purulent exudate, which is an inflammatory exudate rich in leukocytes, mostly neutrophils, debris of dead cells, and, in cases, microbes.
• A transudate or serous pleural effusion gives a clear yellow appearance,is translucent and optically inverted and mainly indicates cardiac or circulatory disease.
• Several mechanisms are responsible for increased permeability of postcapillary venules

Responses of Lymphatic Vessels and Lymph Nodes

• Lymphatics and lymph nodes filter extravascular fluids.
• Lymphatics drain extravascular fluid from capillaries.
• Lymph flow helps drain edema fluid from vascular permeability.
• Leukocytes, cell debris, and microbes use lymph to move.
• Lymphatic vessels proliferate during inflammatory reactions to handle the increased load.
• Lymphatics become secondarily inflamed (lymphangitis).
• Draining lymph nodes (lymphadenitis) are often enlarged due to hyperplasia of the lymphoid follicles and amplified lymphocytes and macrophages.
• These changes termed reactive, or inflammatory, lymphadenitis

Leukocyte Recruitment

• In the lumen, margination results in exit from the center of the bloodstream into the peripheral part.
• Rolling and adhesion occur to endothelium.
• Transmigration involves migration across the endothelium and vessel wall.
• Migration in the tissues occurs towards chemotactic stimulus.
• Review Question #3: 6 year-old comes with infections of Staphylococcus aureus and Streptococcus pneumoniae. There biopsy specimen obtained from an area of soft tissue necrosis shows microbial organisms and very few neutrophils plus a defect in rolling. Selectins are the molecules most likely affected.
• Leukocyte rolling begins the transmigration of neutrophils from the vasculature to the tissues.
• Rolling depends on selectins
• Endothelial cells: P-selectin and E-selectin
• Neutrophils: L-selectin and their sialylated ligands (e.g., sialylated Lewis X)
• Option B: Integrins are involved in the next step of transmigration, during which there is firm adhesion between neutrophils and endothelial cells.
• Option A: Complement C3b acts as an opsonin to facilitate phagocytosis.
• Option C: Leukotriene B4 is a chemotactic agent.
• Option D: NADPH oxidase is involved in phagocytic cell microbicidal activity.

Acute Inflammation: Chemotactic Factors

• Exogenous and endogenous substances like bacterial products and cytokines (especially those of the chemokine family).
• Components of the complement system; C5a and products such as leukotriene B4 of the lipoxygenase pathway of arachidonic acid (AA) metabolism.
• Review Question #4: Which of the following substances most likely has the greatest affinity for neutrophils: C5a.
• Chemotactic Factors: Formylated peptides, Bacterial products of Escherichia coli are chemotactic for Neutrophils.
• C5a is an activated complement component chemotactic for Neutrophils.
• HETE, LTB4 are Leukotrienes chemotactic for Neutrophils
• Kallikrein, the product of factor XIa-mediated
• conversion of prekallikrein is chemotactic for Neutrophils.
• Fibrinogen, a plasma protein is chemotactic for Neutrophils
• PAF is AGEPC and comes from basophils and mast cells.
• PAF Eosinophils
• PDGF from platelets, monocytes-
• macrophages, smooth muscle cells, and endothelial cells is chemotactic to Neutrophils and macrophages
• TGF-βis from platelets, neutrophils, macrophages, lymphocytes, and
• fibroblasts and stimulates Macrophages and fibroblasts
• Fibronectin is an extracellular matrix protein that stimulates Fibroblasts and endothelial cells

Phagocytosis of the Offending Agent

• The two major phagocytes, neutrophils and macrophages.
• Review question #5: 12-month-old boy with a 6-month history of repeated infections has had a fever and cough for the past 3 days.
• Gram stain of sputum shows many gram-positive cocci in chains. CBC shows neutrophilia
• Lab studies show that the patient neutrophils phagocytose and kill organisms promptly in the presence of normal human serum, but not in his own serum
• The neutrophils migrate normally in a chemotaxis assay
• The most likely cause of this boy's increased susceptibility to infection?
  • B. Diminished opsonization
• Correct answer B: This immunoglobulin deficiency prevents opsonization and phagocytosis of microbes.
• Deficiency of integrins and selectins, or a defect in microtubules, prevents adhesion and locomotion of neutrophils.
• Hydrogen peroxide (H2O2) production is part of the oxygen-dependent killing mechanism.
• Opsonization is the coating of particulate material by substances referred to as opsonins.
• Opsonins immobilize the particles on the surface of the phagocyte.
• Main opsonins are IgG subtypes and C3b, a complement component.
• Fragments opsonized by IgG are bound to phagocytic cells by cell-surface receptors for the Fc portion of the IgG molecule.
• Fragments opsonized by C3b bind to cellular receptors for C3b.