In vitro cytocidal effects of human immunodeficiency virus type 1 Nef on unprimed human CD4(+) T cells without MHC restriction

We have previously shown that the C-terminal region of human immunodeficiency virus type 1 (HIV-1) Nef antigen present on the outer surface of virus-infected cells has an affinity for uninfected T cells and that the Nef protein is responsible for T cell death. To exclude completely the possibility of MHC restriction of this cytotoxic activity, the in vitro cytotoxic potential of HIV-1 Nef against various CD4(+) T cell lines as well as naive T lymphocytes was investigated using a baculovirus expression system. Insect cells expressing myristoylated Nef on their cell surface were shown to kill a proportion of CD4(+) T cells within 8 h. However, N-terminal truncated and unmyristoylated Nef proteins were not present on the outer surface of insect cell membranes and failed to show any killing activity. Monoclonal antibodies against the C-terminal region of Nef inhibited cytolysis. Thus, we conclude that specific Nef-mediated cytolysis is induced by contact with unprimed CD4(+) T lymphocytes without MHC restriction.