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EVIDENCE FROM
ANIMAL AND LABORATORY MODELS
A recent study demonstrated that an HIV variant that causes AIDS in humans--HIV-2--also causes a similar syndrome when injected into baboons (Barnett et al., 1994). Over the course of two years, HIV-2-infected animals exhibited a significant decline in immune function, as well as lymphocytic interstitial pneumonia (which often afflicts children with AIDS), the development of lesions similar to those seen in Kaposi's sarcoma, and severe weight loss akin to the wasting syndrome that occurs in human AIDS patients. Other studies suggest that pigtailed macaques also develop AIDS-associated diseases subsequent to HIV-2 infection (Morton et al., 1994). Asian monkeys infected with clones of the simian immunodeficiency virus (SIV), a lentivirus closely related to HIV, also develop AIDS-like syndromes (reviewed in Desrosiers, 1990; Fultz, 1993). In macaque species, various cloned SIV isolates induce syndromes that parallel HIV infection and AIDS in humans, including early lymphadenopathy and the occurrence of opportunistic infections such as pulmonary Pneumocystis carinii infection, cytomegalovirus, cryptosporidium, candida and disseminated MAC (Letvin et al., 1985; Kestler et al., 1990; Dewhurst et al., 1990; Kodama et al., 1993). In cell culture experiments, molecular clones of HIV are tropic for the same cells as clinical HIV isolates and laboratory strains of the virus and show the same pattern of cell killing (Hays et al., 1992), providing further evidence that HIV is responsible for the immune defects of AIDS. Moreover, in severe combined immunodeficiency (SCID) mice with human thymus/liver implants, molecular clones of HIV produce the same patterns of cell killing and pathogenesis as seen with clinical isolates (Bonyhadi et al., 1993; Aldrovandi et al., 1993). |