Acquired Immunodeficiency Syndrome (AIDS)

Acquired Immunodeficiencies

Congenital Immunodeficiencies

Some people are born with a defective immune system. Defects in, or the absence of, a number of inherited genes can result in congenital immunodeficiencies. For example, individuals with a certain recessive trait, DiGeorge's syndrome, do not have a thymus gland and therefore lack cell-mediated immunity.

A variety of drugs, cancers, or infectious agents can result in acquired immunodeficiencies. For example, Hodgkin's disease (a type of cancer) lowers the cell-mediated response. Many viruses are capable of infecting and killing lymphocytes, lowering the immune response. Removal of the spleen decreases humoral immunity. Table 1 summarizes several of the better known immune deficiency conditions.

In 1981, a cluster of cases of Pneumocystis pneumonia appeared in the Los Angeles area. This extremely rare disease usually occurred only in immunosuppressed individuals. Investigators soon correlated the appearance of this disease with an unusual incidence of a rare form of cancer of the skin and blood vessels called Kaposi's sarcoma. The people affected were all young homosexual men, and all showed a loss of immune function. By 1983, the pathogen causing the loss of immune function had been identified as a virus that selectively infects T helper cells. This virus is now known as human immunodeficiency virus, or HIV (Figure l).

Figure 1. Several human immunodeficiency viruses (HIVs), the causative agent of AIDS, budding from a CD4 ⁺ T cell.

Дата добавления: 2015-06-04