MHC-antigens: constituents of the envelopes of human and simian immunodeficiency viruses.

Immunoelectron microscopy was applied to study the antigenic make-up of human and simian immunodeficiency viruses (HIV, SIV) grown in cells expressing either MHC class I (Molt-3) or MHC class I and II (H9) antigens. A variety of antibodies directed against the surface glycoprotein gp120 of HIV and against MHC class I and II antigens were employed. Consistent with earlier observations on the loss of HIV envelope components, gp120 was only weakly demonstrable on the mature virion. MHC class I determinants were present regularly in small amounts on HIV and SIV. Class II antigens, e.g. HLA-DR were found in high density on HIV and SIV grown in H9 cells, but were absent, as expected, on virus grown in Molt-3 cells. These cellular surface antigens are constituents of the virion. The presence of MHC class II antigens in virus preparations used for diagnostic purposes might explain some of the false positive results in HIV serology. Possible biological implications of these virus associated cellular antigens for the pathogenicity of HIV are discussed.