Immune Responses

Question 1

Explain what are the three routes to activate the complement system:

Answer 1

Question 2

Mature, naive B cells prior to being activated express what isotyoes of antibodies?

Answer 2

All isotypes can exist as monomers. Mature, naive B cells prior to activation express IgM and IgD on their surfaces. They may differentiate in germinal centers of lymph nodes by isotype switching (gene rearrangement; mediated by cytokines and CD40L) into plasma cells that secrete IgA, IgE, or IgG.

Question 3

Describe the different part and structures of the antibody:

Answer 3

Question 4

IgG

Only isotype antibody that can cross the placenta and….

Answer 4

• Main antibody in 2° response to an antigen.
• Most abundant isotype in serum.
• Fixes complement, *crosses the placenta (provides infants with passive immunity), opsonizes bacteria, neutralizes bacterial toxins and viruses.

Question 5

IgA

Prevents attachment of bacteria and viruses to mucous membranes and…..

Answer 5

• 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 J chain 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.

Question 6

IgM

Pentamer when J chain when secreted and……

Answer 6

• Produced in the 1° (immediate) response to an antigen.
• Fixes complement but does not 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.

Question 7

IgD

Answer 7

Found on surface of many B cells and in serum

Question 8

IgE

Answer 8

Binds mast cells and basophils; cross-links when exposed to allergen, mediating immediate (type I) hypersensitivity through release of in ammatory mediators such as histamine.

• Mediates immunity to worms by activating eosinophils.
• Lowest concentration in serum.