McKenna's Pharmacology for Nursing, 2e

234

P A R T 3  Drugs acting on the immune system

Plasma cell (IgM)

A

B

Antigen B cell

Antibodies

Memory cell (IgG)

Helper T cells

Antigen

Suppressor T cells

Ag-Ab complex

C

Activation of complement

FIGURE 15.4  The humoral immune response. A. A B cell reacts with a specific antigen to form plasma cells and memory cells, which produce antibodies. B. Circulating antibodies react with the antigen to form an antigen–antibody (Ag-Ab) complex. This process is facilitated by helper T cells and suppressed by suppressor T cells. C. The antigen–antibody

↑ Capillary permeability

Vasodilation

Histamine release

Kinin activation

Chemotaxis Phagocytosis Lysis

Pain

complex activates circulating complement, which facilitates

D

aggressive inflammatory reactions. D. This process destroys the antigen.

Antigen destroyed

form an antigen–antibody complex. This new structure reveals a new receptor site on the antibody that activates a series of plasma proteins in the body called comple­ ment proteins. Complement proteins Complement proteins react in a cascade fashion to form a ring around the antigen–antibody complex. The complement can destroy the antigen by puncturing its membrane, allowing an osmotic inflow of fluid that causes the cell to burst. They also induce chemotaxis (attraction of phagocytic cells to the area), increase the activity of phagocytes and release histamine. Hista­ mine release causes vasodilation, which increases blood flow to the area and brings in all of the components of the inflammatory reaction to destroy the antigen. The antigen–antibody–complement complex precipitates out of the circulatory system and deposits in various sites, including end arteries in joints, the eyes, the kidneys and the skin. The signs and symptoms of the inflamma­ tory response can be seen where the antigen–antibody complexes are deposited. Chickenpox eruptions are an example of an antigen–antibody–complement complex

that deposits in the skin and causes a local inflammatory reaction. Antibody formation The initial formation of antibodies, or primary response, takes several days. Once activated, the B cells form memory cells that will produce antibodies for immedi­ ate release in the future if the antigen is encountered. The antibodies are released in the form of immuno­ globulins. Five different types of immunoglobulins have been identified: • The first immunoglobulin released is M (IgM), which contains the antibodies produced at the first exposure to the antigen. • IgG, another form of immunoglobulin, contains antibodies made by the memory cells that circulate and enter the tissue; most of the immunoglobulin found in the serum is IgG. • IgA is found in tears, saliva, sweat, mucus and bile. It is secreted by plasma cells in the GI and respiratory tracts and in epithelial cells. These antibodies react with specific pathogens that are encountered in exposed areas of the body.