Quantitative and phenotypic analyses of lymphocyte–monocyte heterokaryons induced by the HIV envelope proteins: Significant loss of lymphoid markers

Abstract Cells infected with the human immunodeficiency virus (HIV) can fuse with CD4 + cells leading to the formation of multinucleated cells. The presence of multinucleated cells infected with HIV in tissues of patients has been documented, although their cellular composition and role in AIDS pathogenesis is still under study. Here, we present evidence of in vitro heterotypic lymphocyte–monocyte fusion in cocultures of lymphocytic Jurkat T cells expressing the HIV-1 gp120/gp41 glycoproteins (Env) and CD4 + monocytic THP-1 cells. Using a previously characterized method that involves differential labeling of fusion partners with fluorescent probes and flow cytometry analysis after coculture, up to 20% of double fluorescent cells were detected in 48 h. This double fluorescent cell population was produced by heterotypic lymphocyte–monocyte fusion as it was not observed when Jurkat T cells expressing a mutant non-fusogenic Env protein were used. Heterokaryon formation was inhibited by an anti-CD4 monoclonal antibody and the HIV-fusion inhibitor peptide T-20. About 68% of heterokaryons remained alive and non-apoptotic after 2 days of coculture. In heterokaryons, CD4 was barely detectable and the expression of the CD3 and CD28 lymphoid markers was greatly reduced, whereas the expression of CD32 and the intracellular antigen CD68, both markers of monocytic cells, remained unchanged. In contrast with unfused T cells, heterokaryons only expressed very low levels of the lymphoid activation marker CD25 following treatment with PMA plus ionomycin. These studies point to the possible generation of lymphocyte–monocyte heterokaryons with a myeloid phenotype during HIV infection, with unknown consequences for AIDS pathogenesis.