Neutralizing antibodies modulate replication of simian immunodeficiency virus SIVmac in primary macaque macrophages.

Cultured macaque macrophages are permissive for the replication of SIVmac251, and inoculation with virus is followed by the production of viral p27. Neutralizing macaque polyclonal and murine monoclonal antibodies preincubated with the virus prevented infection but did not prevent cytopathic virus replication when added more than 3 days after inoculation with virus. However, application of the neutralizing antibodies to macrophages 24 h after inoculation with virus resulted in sustained, low-level production of viral antigen. Cell lysates and individual macrophages from treated cultures contained less viral protein by Western blot (immunoblot) and immunocytochemistry than untreated controls. In situ hybridization and polymerase chain reaction procedures for detecting and estimating relative amounts of viral RNA and DNA showed that both viral nucleic acids failed to increase beyond the levels obtained before the addition of neutralizing antibodies. The data suggest that macrophages may need to be infected with a minimum threshold of virus particles in order to reach their full potential for virus replication and that their exposure to neutralizing antibodies prior to reaching this threshold resulted in limited virus replication.