Neutralizing as well as non-neutralizing polyclonal immunoglobulin (Ig)G from infected patients capture HIV-1 via antibodies directed against the principal immunodominant domain of gp41.

We analyzed the factors influencing the binding of polyclonal immunoglobulin (Ig)G from HIV-infected patients to primary isolates (PI) in capture assays and a potential correlation between this binding and neutralization. The fixation of antibodies (Abs) to viral particles was measured by quantifying the capture of 4 PI by purified IgG immobilized onto a plate or by analyzing the capture of IgG-virus complexes formed in solution. We found that the capture of virus and the formation of immune complexes is mainly achieved by Abs directed against the principal immunodominant domain (PID) of gp41. We have further compared the binding measured by these two methods and the neutralizing activity of our polyclonal IgG and found no correlation. Thus, capture assays, including the immune complex capture assay that is more representative of "physiological" conditions, cannot be used as surrogate method for the investigation of the neutralizing activity of Abs.