Immunology

Question 1

MHC I

Answer 1

(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

Question 2

MHC II

Answer 2

(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

Question 3

B Cells

Answer 3

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.

Question 4

T Cells

Answer 4

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).

Question 5

Innate Immunity

Answer 5

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

Question 6

Adaptive Immunity

Answer 6

T cells, B cells, circulating antibodies
Variation through V(D)J recombination during lymphocyte development
Secreted: Immunoglobulins

Question 7

Interleukin - 1

Answer 7

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.

Question 8

Interleukin - 6

Answer 8

Cytokine - secreted by macrophages

Causes fever and stimulates production of acute-phase proteins.

Question 9

Interleukin - 8

Answer 9

Cytokine - secreted by macrophages

Major chemotactic factor for neutrophils.

Question 10

Interleukin - 12

Answer 10

Cytokine - secreted by macrophages

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

Question 11

Interleukin - 2

Answer 11

Cytokine - secreted by all T Cells

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

Question 12

Interleukin - 3

Answer 12

Cytokine - secreted by all T Cells

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

Question 13

Interleukin - 4

Answer 13

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.

Question 14

Interleukin - 5

Answer 14

Cytokine - secreted by Th2 Cells
Promotes growth and differentiation of B cells.
Enhances class switching to IgA. Stimulates growth and differentiation of eosinophils.

Question 15

Interleukin - 10

Answer 15

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.

Question 16

Tumor necrosis factor - alpha

Answer 16

Cytokine - secreted by macrophages

Activates endothelium. Causes WBC recruitment, vascular leak.

Question 17

Interferon - gamma

Answer 17

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.

Question 18

IgG

Answer 18

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).

Question 19

IgA

Answer 19

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.

Question 20

IgM

Answer 20

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.

Question 21

IgD

Answer 21

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

Question 22

IgE

Answer 22

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.