Antibody Response in Primary Human Immunodeficiency Virus Infection

The antibody response in 20 homosexual men with symptomatic primary HIV infection was studied with ten different antibody assays (enzyme-linked immunosorbent assays, indirect immunofluorescence assays, radioimmunoprecipitation [RIPA], and western blot). HIV antibodies were detectable by all the assays within 2 months after onset of illness. RIPA and western blot were more sensitive than the other assays--all serum samples obtained at 2 weeks and after were reactive. In all cases, the first serum sample reactive by RIPA precipitated gp160 whereas, by western blot, antibodies to p24 were first recognised. This study shows the necessity of including gp160 and p24 in any assay to detect early antibody response in primary HIV infection. 5 patients were studied by virus isolation. During the 2 first weeks after onset of symptoms, HIV was demonstrated in cell-free plasma in all cases and, in 4 cases, also in peripheral blood mononuclear cells. Samples obtained later contained demonstrable infectious virus in only 1 of 4 cases. Thus a phase of viraemia precedes the antibody response in symptomatic primary HIV infection.