Human immunodeficiency virus (HIV) complexed with human anti-HIV
IgG can attach to
Fc gamma receptors (Fch) of mononuclear phagocytes. To determine whether the FcR-mediated
infection that results also requires interaction between HIV gp120 and cell membrane CD4, monocytic cells of the U937 line were transiently treated with
phorbol 12,13-dibutyrate (PDB) so that they temporarily presented a CD4-FcR+ phenotype at the time of
HIV infection. HIV production was not abolished, but only significantly delayed after
infection of these cells with free virus. Leu3a
monoclonal antibody or soluble recombinant CD4 completely blocked this delayed
infection. This indicates that enough CD4 still remained at the membrane to allow
infection of a reduced cell number.
Infection of PDB-treated cells with virus preincubated with high anti-HIV
IgG concentrations was inhibited, contrasting with what was observed with control cells infected under the same conditions. Inhibition of
infection was also observed when HIV became attached to untreated U937 cells through the binding of
CD4-IgG hybrid molecules to FcR. Thus, the binding of
IgG-coated virus to FcR is not sufficient in itself to elicit productive
infection of monocytic cells, which still requires the interaction of viral gp120 and membrane CD4.