CH 21E : Immune System- B cells

Humoral Immunity

INDIRECT method of defense

• B cells produce antibodies that bind to antigens and tag them for destruction

B cell development

in the bone marrow

B cell selection (homeschooled)

stay in bone marrow

• B cells that react to self antigens undergo apoptosis

Self tolerant B cells

Synthesize antigen surface receptors, divide rapidly, and then produce immunocompetent clones

B cell deployment

leave bone marrow and colonize same lymphatic organs and tissues as T cells

Antigen Recognition (B cell activation Step 1)

Immunocompetent B cells exposed to antigen. Antigen binds to ONLY B cell with complement receptors.

Antigen Presentation (Step 2 B cell activation)

B cell internalizes antigen and displays processed epitope. Helper T cells bind to B cells and secrete Interleukin.

Clonal Selection (B cell activation Step 3)

Interleukin stimulates B cell to divide repeatedly and form a clone.

Differentiation (B cell activation STEP 4)

Some cells of the clones become memory B cells, most differentiate into plasma cells.

Attack (B cell activation STEP 5)

Plasma cells synthesize and secrete antibody. Antibody employs various means to render antigen harmless

Plasma Cells

• Longer, more rough ER

• Live 4-5 days

• Secrete 2000 molecule per sec

• Antibody factory (due to rough ER)

Antibodies

Immunoglobulins, Y-Shaped molecule with variable and constant regions

Immunoglobulins (Igs)

Defensive gamma globulins

• Blood, plasma, tissue fluids, secretions, membranes

Variable regions of antibody

antigen specfic

Constant regions of antibody

same with each class and detirmines the action

5 Immunoglobulin Classes

• IgA

• IgD

• IgE

• IgG

• IgM

Somatic Recombination

Genetic recombination produces endless combinations of antibody genes

Somatic Hypermutation

process that introduces mutations into B cells to help them adapt to foreign elements

IgA

Secretory antibody; NATURAL PASSIVE IMMUNITY (breast milk)

• Monomer in blood plasma

• Dimer in mucus, tears, milk, saliva

IgD

Receptors on B cells. Function in activated of B cells via antigens

• Monomer

IgE

Receptor in basophils and mast cells; Responsible in Type 1 Hypersensitivities

• monomer

IgG

Most abundant and smallest; long term immunity and natural passive immunity via placenta

• SECONDARY.

• HEMOLYTIC DISEASE

• Monomer

IgM

Largest; Primary immune response.

• Transfusion reactions (ABO)

• Monomer and Pentamer