Humoral Effector Functions

Question 1

Humoral Immunity

Answer 1

Branch of adaptive immunity mediated by Ab produced by B cells and plasma cells

Humoral immunity is the principle defense against extracellular pathogens because Ab in circulation

Question 2

General Concepts

Answer 2

• Abs are produced by plasma cells in the lymphoid tissues/organs. The Abs perform their function at sites distant from production
• The effector functions of Abs are mediated by the Fc region. Different isotherm serve different effector functions
• Although the effector functions are mediated through the Fc region ALL FUNCTIONS ARE TRIGGERED BY THE BINDING OF AG TO THE Fab (V) REGION

Question 3

Adaptive Immune Response

Answer 3

Primary Ab response
Lag after immunization- usually 5-10 days
Peak Response- smaller
Ab Isotype- usually IgM>IgG
Ab Affinity- lower average affinity, more variable

Secondary Response
Lag after immunization- usually 1-3 days
Peak Response- larger
Ab Isotype- relative increase in IgG and under certain situations, in IgA or IgE heavy chain isotype switching)
Ab Affinity- higher average affinity (affinity maturation)

Question 4

Effector Functions

Answer 4

B cell binds with a microbe —> Ab secreted
—> antibodies - neutralization of microbes
—> Fc receptor- opsonization and phagocytosis of microbes
—> NK cell binds with Ab and microbe - Ab dependent cellular cytotoxicity
—> —> complement activation
—>C3b receptor -phagocytosis of microbes opsonization with complement fragments/inflammation/lysis of microbes

Question 5

Antibody Effector Functions

Answer 5

• Isotype switching diversities functional properties
• Fc region contains binding sites for complement and Fc receptors (FcR)

-Fc region serves two distinct functions
—deliver Ab to inaccessible anatomical sites
-Link bound Ag to molecules/cells that effect destruction of pathogen

Question 6

What do Ag bound Ab do?

Answer 6

Antigen bound Ab will find to Fc receptors (FcR) in order to act as poisonings or to activate cells!

Question 7

Neutralization

Answer 7

Many microbes bind to the surfaces of cells to gain entry

Ab neutralizes the infectivity an potential effects of infection

Abs may sterically hinder binding of microbes

Only requires binding of Ag, any class of Ab works

The higher the affinity, the better