The Relationship between the Human Immunodeficiency Virus and the Acquired Immunodeficiency Syndrome (Draft)

DRAFT
The acquired immunodeficiency syndrome (AIDS) is characterized by the progressive
loss of the CD4+ helper/inducer subset of T lymphocytes, leading to severe
immunosuppression and constitutional disease, neurologic complications, and opportunistic
infections and neoplasms that rarely occur in persons with intact immune function. Although
the precise mechanisms whereby the immune system is destroyed have not been fully
delineated, abundant epidemiologic, virologic and immunologic data clearly indicate that
infection with the human immunodeficiency virus (HIV) is the underlying cause of AIDS. This
discussion reviews the AIDS epidemic and summarizes the evidence supporting HIV as the
cause of AIDS.
Emergence of AIDS
In 1981, clinical investigators in New York and Califomia observed among young,
previously healthy, homosexual men an unusual clustering of cases of rare diseases, notably
Kaposi's sarcoma (KS) and opportunistic infections such as Pneumocystis carinii pneumonia
(PCP), as well as cases of unexplained, persistent lymphadenopathy (CDC, 1981 a, 1981 b,
1982a; Masur et al., 1981; Gottlieb et al., 1981; Siegal et al., 1981). It soon became evident
that these men had a common immunologic deficit, an impairment in cell-mediated immunity
resulting from a significant loss of "T-helper" cells, which bear the CD4 marker (Gottlieb et al.,
1981; Friedman-Kien, 1981; Masur et al., 1981; Ammann et al., 1983a).
The widespread occurrence of KS and PCP in young people with no underlying
disease or history of immunosuppressive therapy was unprecedented. Searches of the
medical literature, autopsy records and tumor registries revealed that these diseases
previously had occurred at very low levels in the United States (Walzer et al., 1974; CDC,
1981b; ODO, 1982f).
KS, a very rare skin neoplasm, had affected mostly older men of Mediterranean origin
or cancer or transplant patients undergoing immunosuppressive therapy (Gange and Jones,
1978; Safai et al., 1981). Before the AIDS epidemic, the annual incidence of Kaposi's