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FIRST AID IMMUNOLOGY > Immune Responses > Flashcards

Flashcards in Immune Responses Deck (30):
1

IgG

Main antibody in 2° response to an 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).

2

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 (eg, Giardia). 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

3

IgM

Produced in the 1° (immediate) response to an antigen. Fixes complement. Cannot cross the placenta. Antigen receptor on the surface of B cells. Monomer on B cell, pentamer with J chain when secreted. Pentamer enables avid binding to antigen while humoral response evolves.

4

IgD

Unclear function. Found on surface of many B cells and in serum

5

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. Lowest concentration in serum

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Classic Complement Pathway

IgG or IgM mediated

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Alternative Complement Pathway

microbe surface molecules

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Lectin Complement Pathway

mannose or other sugars on microbe surface

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C3b functions

opsonization

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C3a, C4a, C5a functions

anaphylaxis

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C5a functions

neutrophil chemotaxis

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C5b-9 functions

cytolysis by MAC

13

Opsonins functions

C3b and IgG are the two 1° opsonins in bacterial defense; enhance phagocytosis. C3b also helps clear immune complexes.

14

Inhibitors functions

decay-accelerating factor (DAF, aka CD55) and C1 esterase inhibitor help prevent complement activation on self cells (eg, RBCs).

15

Early complement deficiencies (C1-C4)

Increased risk of severe, recurrent pyogenic sinus and respiratory tract infections. Increased risk of SLE

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Terminal complement deficiencies (C5–C9)

Increased susceptibility to recurrent Neisseria bacteremia

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C1 esterase inhibitor deficiency

Causes hereditary angioedema due to unregulated activation of kallikrein ->
bradykinin.

Characterized by decreased C4 levels.

ACE inhibitors are contraindicated.

18

Paroxysmal nocturnal hemoglobinuria

A defect in the PIGA gene preventing the formation of anchors for complement inhibitors, such as decay-acclerating factor (DAF/CD55) and membrane inhibitor of reactive lysis (MIRL/CD59). Causes complement-mediated lysis of RBCs

19

IL-1

SECRETED BY MACROPHAGES

Causes fever, acute inflammation. Activates endothelium to express adhesion molecules. Induces chemokine secretion to recruit WBCs. Also known as osteoclast-activating factor.

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IL-6

SECRETED BY MACROPHAGES

Causes fever and stimulates production of acutephase proteins

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IL-8

SECRETED BY MACROPHAGES

Major chemotactic factor for neutrophils

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IL-12

SECRETED BY MACROPHAGES

Induces differentiation of T cells into Th1 cells. Activates NK cells

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Tumor necrosis factor-alpha

SECRETED BY MACROPHAGES

Activates endothelium. Causes WBC recruitment, vascular leak

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IL-2

SECRETED BY ALL T CELLS

Stimulates growth of helper, cytotoxic, and regulatory T cells, and NK cells

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IL-3

SECRETED BY ALL T CELLS

Supports growth and differentiation of bone marrow stem cells. Functions like GM-CSF

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INF-gamma

FROM Th1 CELLS

Secreted by NK cells and T cells in response to antigen or IL-12 from macrophages; stimulates macrophages to kill phagocytosed pathogens. Inhibits differentiation of Th2 cells

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IL-4

FROM Th2 CELLS

Induces differentiation of T cells into Th (helper) 2 cells. Promotes growth of B cells. Enhances class switching to IgE and IgG

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IL-5

FROM Th2 CELLS

Promotes growth and differentiation of B cells. Enhances class switching to IgA. Stimulates growth and differentiation of eosinophils.

29

IL-10

FROM Th2 CELLS

Attenuates inflammatory response. Decreases expression of MHC class II and Th1 cytokines. Inhibits activated macrophages and dendritic cells. Also secreted by regulatory T cells

30

Interferon-α and -β

A part of innate host defense against both RNA and DNA viruses. Interferons are glycoproteins synthesized by virus-infected cells that act on local cells, “priming them” for viral defense by downregulating protein synthesis to resist potential viral replication and upregulating MHC expression to facilitate recognition of infected cells.