Microscopic analysis of interactions between HIV particles and living leukocytes

Video-enhanced/-intensified optical microscopy has been used to study the interaction of non-infectious HIV8E5 particles with living cells. The purified particles retained gp120 antigenic sites. Fluorescent lipids were intercalated into the particles' envelopes. When incubated with CD4+ cell lines, roughly 90% of the cells bound HIV8E5 particles. The extent of fusion and endocytosis varied among the cell lines tested. CD4- control cells did not significantly bind, fuse, or internalize particles. To control for non-specific exchange of the fluorescent label, HIV8E5 were bound to CD4- murine WEHI cells using concanavalin A; no apparent fusion or internalization took place. We suggest that both fusion and internalization are important mechanisms of virion-cell interaction. Adherent human peripheral blood mononuclear cells were much less efficient in binding HIV8E5 than non-adherent mononuclear cells. Both endocytosis and apparent fusion were observed for lymphocytes. Our results indicate that cells interact with HIV8E5 by multiple pathways and that these pathways are strongly affected by cell type (lymphocyte or monocyte) and origin (normal or transformed). These methods may be useful in characterizing viral entry and in anti-viral drug screening.