B Lymphocyte Effector Functions

What are the B cell effector cells?

Plasma cells

What do plasma cells secrete?

Antibodies – only secrete the class of antibody they class switch to

What do antibodies bind?

Antigen and form an immune complex

How many times do antibodies class switch

1

What are the antibody effector functions?

1. Neutralize pathogens

2. Agglutination (clump) of pathogens

3. Opsonization

4. Complement activation

5. Antibody-dependent cell-mediated cytotoxicity (ADCC)

6. Degranulation

What is the antibody structure?

Antibody structure:

-Fab – binds to antigen each antibody has 2 of these

-Fc – binds to Fc receptors on other immune cells

      - Fc receptors signal to immune cells when the antibody is bound to antigen

Fc receptors bind to specific antibodies, not one size fits all

How is the function of Neutralizing Antibodies done?

Antibody binds antigen and prevents it from entering other cells

How is the function of Agglutination done?

Crosslinking of multiple pathogens results in clumping of pathogen

Cross linking: each Fab portion of an antibody binds to a different pathogen

How is the function of Opsonization done?

Fc part of antibody of an immune complex will bind to Fc receptor on phagocytic cell and initiate phagocytosis

How is the function of Complement Activation done?

Immune complex binds complement initiator proteins which activate the classical pathway of complement

Results in inflammation, lysis of microbes through membrane attack complex, and opsonization

How is the function of Antibody-Dependent Cell-mediated Cytotoxicity done?

-Fc part of antibody binds to Fc receptor on NK cells

-When antigen binds to Fab part of antibody on NK cell, the NK cell will become cytotoxic

-Results in secretion of granzyme and perforin and FasL binding to Fas to initiate apoptosis of infected cell

How is the function of Antibody-Activated Degranulation done?

-Fc part of an immune complex binds to Fc receptor on a granulocyte

-Contents of cytoplasmic granules are released from cell

-Some contents of granules are harmful to pathogens and some promote inflammation

What antibody class is never secreted?

IgD

How is IgM secreted?

Secreted as a pentamer

What is IgM good at?

agglutination and neutralization

What functions can’t IgM do?

cannot do any function requiring an Fc receptor

How is IgG secreted?

Secreted as a monomer (probably the most common)

What is IgG good at?

opsonization, activating complement, and ADCC

How is IgE secreted?

secreted as a monomer

What is IgE good at?

degranulation

How is IgA secreted and what is it good at in each location?

Secreted as a dimer and tetramer in mucosal tissue

       - good at neutralization, and agglutination

- secreted as a monomer in rest of body

        - good at ADCC and degranulation