Immunology Flashcards
MHC I
(Major histocompatibility complex I)
1 long chain, 1 short chain
Expressed on all nucleated cells, APCs, platelets (except RBCs)
Presents endogenous antigens (eg, viral or cytosolic proteins) to CD8+ cytotoxic T cells
MHC II
(Major histocompatibility complex II)
2 equal length chains (2 alpha, 2 beta)
Expressed on APCs
Presents exogenous antigens (eg, bacterial proteins) to CD4+ helper T cells
B Cells
Humoral Immunity
Recognize and present antigen - undergo somatic hypermutation to optimize antigen specificity.
Produce antibody - differentiate into plasma cells to secrete specific immunoglobulins.
Maintain immunologic memory - memory B cells persist and accelerate future response to antigen.
T Cells
Cell-mediated Immunity
CD4+ T cells help B cells make antibodies and produce cytokines to recruit phagocytes and activate other leukocytes.
CD8+ T cells directly kill virus-infected and tumor cells via perforin and granzymes (similar to NK cells).
Innate Immunity
Neutrophils, macrophages, monocytes, dendritic cells, natural killer (NK) cells (lymphoid organ), complement, physical epithelial barriers, secreted enzymes
Germline encoded
Secretes: lysozyme, complement, C-reactive protein (CRP), defensins, cytokines
Adaptive Immunity
T cells, B cells, circulating antibodies
Variation through V(D)J recombination during lymphocyte development
Secreted: Immunoglobulins
Interleukin - 1
Cytokine - secreted by macrophages
Causes fever, acute inflammation. Activates endothelium to express adhesion molecules.
Induces chemokine secretion to recruit WBCs.
Also called osteoclast-activating factor.
Interleukin - 6
Cytokine - secreted by macrophages
Causes fever and stimulates production of acute-phase proteins.
Interleukin - 8
Cytokine - secreted by macrophages
Major chemotactic factor for neutrophils.
Interleukin - 12
Cytokine - secreted by macrophages
Induces differentiation of T cells into Th1 cells. Activated NK cells.
Interleukin - 2
Cytokine - secreted by all T Cells
Stimulated growth of helper, cytotoxic, and regulatory T cells, and NK cells
Interleukin - 3
Cytokine - secreted by all T Cells
Supports growth and differentiation of bone marrow stem cells. Functions like GM-CSF
Interleukin - 4
Cytokine - secreted by Th2 Cells Induces differentiation of T cells into Th 2 cells. Promotes growth of B cells. Enhances class switching to IgE and IgG.
Interleukin - 5
Cytokine - secreted by Th2 Cells
Promotes growth and differentiation of B cells.
Enhances class switching to IgA. Stimulates growth and differentiation of eosinophils.
Interleukin - 10
Cytokine - secreted by Th2 Cells
Attenuated inflammatory response. Decreases expression of MHC class II and Th1 cytokines.
Inhibits activated macrophages and dendritic cells. Also secreted by regulatory T Cells.
Tumor necrosis factor - alpha
Cytokine - secreted by macrophages
Activates endothelium. Causes WBC recruitment, vascular leak.
Interferon - gamma
Cytokine - secreted by Th1 Cells
Secreted by NK cells and T cells in response to antigen or IL-12 from macrophages; stimulated macrophages to kill phagocytosed pathogens.
Inhibits differentiation of Th2 cells.
IgG
Main antibody in secondary response to antigen. Most abundant isotype in serum. Fixes complement, opsonizes bacteria, neutralizes bacterial toxins and viruses. Only isotype that crosses the placenta (provides infants with passive immunity that starts to wane after birth).
IgA
Prevents attachment of bacteria and viruses to mucous membranes; does not fix complement.
Monomer (in circulation) or dimer (with J chain when secreted). Crosses epithelial cells by transcytosis. Produced in GI tract (eg, by Peyer patches) and protects against gut infections. Most produced antibody overall, but has lower serum concentrations. Released into secretions (tears, saliva, mucus) and breast milk. Picks up secretory component from epithelial cells, which protects the Fc portion from luminal proteases.
IgM
Produced in the primary (immediate) response to an antigen. Fixes complement. Antigen receptor on the surface of B cells. Monomer on B cells, pentamer with J chain when secreted. Pentamer enables avid binging to antigen while humoral response evolves.
IgD
Unclear function. Found on surface of many B cells and in serum.
IgE
Binds mast cells and basophils; cross-links when exposed to allergen, mediating immediate (type I) hypersensitivity through release of inflammatory mediators such as histamine. Contributes to immunity to parasites by activating eosinophils.
