Microbiology Demystified

IgA

IgA immunoglobulinis the most common antibody in body secretions and in

mucous membranes. It consists of about 15 percent of the antibodies in a serum.

IgA protects infants from gastrointestinal infections and fights antigens that

affect the respiratory tract. Plasma cells in the mucous membrane form secretory

IgA, which is then passed through the mucosal cell and attacks antigens on the

mucosal surface such as bacteria and viruses. IgA is short-lived

IgD

IgD immunoglobulinis found in blood and lymph fluid and is an antigen re-

ceptor on the surface of B cells. This also provides protection against para-

sitic worms.

IgE

IgE immunoglobulinbinds to basophil cells and mast cells that release chemical

mediators, such as histamine, that cause an allergic reaction. When pollen is the

antigen, the allergic reaction is referred to as hay fever. IgE is less than one per-

cent of serum antibodies. This provides protection against parasitic worms.

B Cells

B cellsare cells that develop from stem cells in the bone marrow and the liver

of fetuses. They are transported to the lymph nodes and spleen where they use

antigen receptors, also known as antigen-binding sites, on the cell’s surface to

seek out antigens.

Once an antigen is detected, the B cell with T cells activates a special group

of lymphocytes that produces antibodies used in the antibody-mediated immu-

nity response. T cells do not make antibodies. When B cells come in contact with

extracellular antigens, the B cell transforms into plasma cells, that produce anti-

bodies at about 2,000 antibodies per second to combat that antigen.

(^216) CHAPTER 14 Immunity