Major histocompatibility gene products and human immunodeficiency virus infection.

In the present paper we analyze the role of major histocompatibility gene products, the human leukocyte antigens, in the pathophysiology of the acquired immunodeficiency syndrome. No association has been found between human leukocyte antigen (HLA) frequencies and human immunodeficiency virus type 1 (HIV 1) infection, whereas significant associations have been reported in some populations between some HLA haplotypes and the appearance of either opportunistic infections or secondary cancers. With regard to the human leukocyte class I antigens, their role as restriction elements in presenting HIV 1 to virus-specific cytotoxic T lymphocytes seems to be established. An increase in the serum levels of their soluble forms that correlate with disease stage has also been demonstrated. These circulating molecules could interfere with the immune response to HIV 1 and could contribute to the development of the immunodeficiency. Antigenic similarities have been detected between human leukocyte class II antigens and HIV 1 envelope proteins. These homologies could explain both the presence in some HIV-positive sera of anti-HLA class II antibodies that mediate the lysis of CD4(+)-HLA class II+ T cells and the false-positive reaction of some HIV-negative sera, which contain anti-HLA class II antibodies, in tests for HIV 1 antibodies. Reduced levels of some complement factors (the human leukocyte class III antigens) have been detected in HIV-infected subjects. These defects could play a role in the progression of the disease and affect both the clearance of HIV 1 and complement-mediated antibody responses. The data reported in this review suggest that HLA antigens may be involved in several steps of the immune deficiency of HIV-infected subjects and thus contribute to the pathophysiology of acquired immunodeficiency syndrome.