Human immunodeficiency virus glycoprotein-specific CD4+ cytotoxic T lymphocytes are involved in two types of cytotoxicity: antigen-specific and cell-cell fusion-related cell lysis.

Human immunodeficiency virus (HIV) glycoprotein-specific CD4+ cytotoxic T lymphocytes (CTLs) lyse target cells in an MHC-restricted calcium-dependent fashion similar to the mechanism used by CD8+ CTLs. However, contact of unprimed peripheral blood CD4+ T cells with HIV glycoprotein-expressing cells has been shown to cause, in addition to cell-cell fusion, rapid cytolysis that may resemble antigen-specific cytotoxicity in the chromium release assay. In this study, the ability of glycoprotein-specific CD4+ CTLs to undergo similar fusion-related cytolysis was examined. The data obtained demonstrate that in addition to antigen-specific calcium-dependent cytotoxicity, envelope-specific CD4+ CTLs are involved in fusion-related, calcium-independent cytolysis.