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Questions and Answers
What is the study of a host's reactions to foreign substances that are introduced into the body called?
Immunology
Louis Pasteur observed that older bacterial cultures accidentally left out on a laboratory bench would not cause disease when injected into chickens because they were _____________.
attenuated
What are the two major branches of immunity mentioned in the text?
Neutrophils are key cells in the adaptive immune system.
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What is the most important role of eosinophils?
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Basophils have a long life span in the bloodstream.
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What is the main function of macrophages in the immune system?
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Plasma cells represent the most fully differentiated _ lymphocyte.
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Where are T lymphocytes mainly localized in lymph nodes?
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What is the interior of a secondary follicle in a lymph node known as?
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Plasma cells actively secrete antigens.
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The skin is considered the largest organ in the body and the epidermis contains several _______ lymphocytes.
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Match the following immune cells with their functions:
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What are the three main subtypes of T cells distinguished based on their unique functions?
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NK cells need prior exposure to target cells to kill them.
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What is the typical ratio of CD4+ to CD8+ cells in peripheral blood?
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T cells bearing the CD4 receptor are mainly either Th or ______ cells.
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Match the following cell types with their descriptions:
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Study Notes
Immunology and Immunity
- Immunology is the study of a host's reactions to foreign substances introduced into the body.
- Antigens are foreign substances that induce a host response, varying from substances like pollen to serious bacterial pathogens.
History of Immunology
- The first recorded attempts to induce immunity date back to the 15th century, with people inhaling powder made from smallpox scabs.
- Edward Jenner successfully prevented infection with smallpox by injecting a less harmful substance, cowpox, in the late 1700s.
- Louis Pasteur discovered the first attenuated vaccine, marking the birth of immunology.
Innate and Adaptive Immunity
- Innate immunity is a natural, non-specific defense against infection, involving mechanisms such as phagocytosis.
- Adaptive immunity is a specific, acquired resistance to infection, characterized by memory and specificity.
- Both systems are necessary for good health and operate in combination.
Cells of the Innate Immune System
- Leukocytes, or white blood cells, play a key role in both innate and adaptive immunity.
- There are five principal types of leukocytes: neutrophils, eosinophils, basophils, monocytes, and lymphocytes.
- Neutrophils:
- Represent 50-70% of peripheral WBCs in adults.
- Engage in phagocytosis, destroying foreign particles.
- Contain neutral staining granules with antimicrobial products.
- Eosinophils:
- Make up 1-4% of peripheral WBCs in non-allergic individuals.
- Engage in phagocytosis, but are less efficient than neutrophils.
- Contain orange to reddish-orange granules with proteins, cytokines, and growth factors.
- Basophils:
- Least numerous of WBCs, making up less than 1% of peripheral WBCs.
- Contain coarse, densely staining granules with histamine, cytokines, and growth factors.
- Regulate adaptive immune responses and stimulate B cells to produce IgE.
- Monocytes:
- Largest cells in peripheral blood, with a diameter of 12-20 µm.
- Contain irregularly folded or horseshoe-shaped nucleus.
- Make up 2-10% of peripheral WBCs.
- Differentiate into macrophages in the tissues.
- Macrophages:
- Arise from monocytes.
- Engage in phagocytosis, microbial killing, and anti-tumor activity.
- Present antigens to T lymphocytes.
- Mast cells:
- Tissue-resident cells, resembling basophils.
- Contain serine proteases, heparin, and neutrophil chemotactic factor.
- Play a role in allergic reactions and function as antigen-presenting cells.
Cells of the Adaptive Immune System
- Lymphocytes:
- Represent 20-40% of peripheral WBCs.
- Arose from an HSC and further differentiated in primary lymphoid organs.
- Divided into three major populations: T cells, B cells, and innate lymphoid cells (NK cells).
- T cells:
- 61-80% of peripheral lymphocytes.
- Involved in cell-mediated immunity.
- B cells:
- 10-20% of peripheral lymphocytes.
- Involved in humoral immunity.
- Natural Killer (NK) cells:
- 10-15% of peripheral lymphocytes.
- Involved in innate immunity.### Clusters of Differentiation (CD)
- Panels of antibodies from different laboratories are used to analyze and define CD
- Each antigen or CD is assigned a number, with over 400 CD designations currently recognized
- Table 1-1 lists important CD numbers used to identify lymphocytes
B Cells and Plasma Cells
- B cells are derived from a lymphoid precursor that differentiates to become a T cell, B cell, or NK cell depending on exposure to different cytokines
- B cells remain in the environment provided by bone marrow stromal cells
- B cells generate highly specific cell surface receptors through genetic recombination of their immunoglobulin genes
- End result: B lymphocyte programmed to produce a unique antibody molecule
- Surface proteins on B cells include membrane-bound antibodies (IgM and IgD), CD19, CD20, CD21, and class II MHC molecules
T Cells
- T lymphocytes are named because they differentiate in the thymus
- Lymphocyte precursors (thymocytes) enter the thymus from the bone marrow and mature into T cells expressing unique surface markers
- T cells have multiple roles in the immune system:
- Produce cytokines that stimulate B cells to make antibodies
- Kill tumor cells and virus-infected cells
- Regulate innate and adaptive immune responses
- Three main subtypes of T cells:
- Helper T cells (Th)
- Cytotoxic T cells (Tc)
- Regulatory T cells (Treg)
- All T cells possess the CD3 marker on their cell surface
- T-cell subtypes can be identified by the presence of either CD4 or CD8
Innate Lymphoid Cells and Natural Killer Cells
- Innate lymphoid cells are a family of related cells that have important roles in innate immunity and tissue remodeling
- Characteristics of innate lymphoid cells:
- Lymphoid morphology
- No antigen-specific receptors
- No myeloid and dendritic cell markers
- Natural killer (NK) cells are a principal type of innate lymphoid cell
- NK cells:
- Do not require the thymus for development
- Mature in the bone marrow
- Have the ability to kill target cells without prior exposure
- Express a specific combination of antigens, including CD16 and CD56
Organs of the Immune System
- Primary lymphoid organs:
- Bone marrow
- Thymus
- Secondary lymphoid organs:
- Spleen
- Lymph nodes
- Mucosal-associated lymphoid tissues (MALT)
- Cutaneous-associated lymphoid tissues (CALT)
- Primary lymphoid organs: where maturation of B lymphocytes and T lymphocytes takes place
- Secondary lymphoid organs: where contact with foreign antigens takes place
Bone Marrow
- Considered the largest tissue in the body
- Fills the core of all long flat bones
- Main source of hematopoietic stem cells (HSCs)
- Develops into erythrocytes, granulocytes, monocytes, platelets, and lymphocytes
Thymus
- Small, flat, bilobed organ found in the thorax
- T cells develop their identifying characteristics in the thymus
- Maturation of T cells takes place during a 3-week period
- Each lobe of the thymus is divided into smaller lobules filled with epithelial cells
- Mature T lymphocytes are released from the medulla
Spleen
- Largest secondary lymphoid organ
- Located in the upper-left quadrant of the abdomen
- Surrounded by a thin capsule of connective tissue
- Divided into two main types: red pulp and white pulp
- Red pulp: makes up more than one-half of the total volume, rich in macrophages
- White pulp: comprises approximately 20% of the total weight, contains lymphoid tissue
- Spleen filters antigens from the blood
Lymph Nodes
-
Serve as central collecting points for lymph fluid from adjacent tissues
-
Located along lymphatic ducts
-
Especially numerous near the joints and where the arms and legs join the body
-
Organization of the lymphoid tissue:
- T cells surround arterioles in the PALS
- B cells are just beyond in follicles
- When stimulated by antigens, B cells form germinal centers
- All the lymphoid tissue is referred to as the white pulp### Immune System
-
Immunity has two branches: innate immunity and adaptive immunity.
-
Innate immunity is the ability of the body to resist infection through preexisting barriers or nonspecific mechanisms that can be activated quickly.
-
Adaptive immunity is characterized by specificity for antigen, memory, and dependence upon lymphocytes.
Adaptive Immune Responses
- There are two main types of adaptive immune responses: humoral immunity and cell-mediated immunity.
- Humoral immunity involves production of antibodies by B lymphocytes and plasma cells.
- Cell-mediated immunity is carried out by T lymphocytes to destroy internal pathogens.
Blood Cells
- All blood cells arise from multipotent HSCs in the bone marrow during hematopoiesis.
- The five principal types of leukocytes are:
- Neutrophils
- Eosinophils
- Basophils
- Monocytes
- Lymphocytes
Tissue Cells
- Mast cells, dendritic cells, and macrophages (arising from monocytes) are involved in immunity.
- Cells involved in the innate immune response and are actively phagocytic include:
- Neutrophils
- Monocytes
- Macrophages
- Dendritic cells
Lymphocytes
- Lymphocytes are the key cells involved in the adaptive immune response because they have antigen-specific receptors.
- B cells are a type of lymphocyte that develop in the bone marrow and are capable of secreting antibody when they mature into plasma cells.
- T cells acquire their specificity in the thymus and consist of two subtypes: CD4+ (mainly Th or Treg cells) and CD8+ ( Tc cells).
- NK cells are lymphocytes that arise from a lymphocyte precursor but do not develop in the thymus.
Lymphoid Organs
- In humans, the bone marrow and the thymus are considered the primary lymphoid organs where lymphocytes mature.
- Secondary lymphoid organs include the spleen, lymph nodes, MALT, and CALT, where lymphocytes come into contact with foreign antigens and become activated in the adaptive immune response.
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Description
Explore the fundamentals of immunology, including the study of host reactions to foreign substances and the immune system's response to antigens.
