Detection and enumeration of circulating HIV-1-specific memory B cells in HIV-1-infected patients

Memory B cells are long-living cells that circulate throughout the body and differentiate into plasma cells after stimulation by antigens, cytokines, and direct cell-to-cell interaction in lymphoid tissues. For HIV-1-infected patients, we assessed whether in vitro polyclonal B cell activation that induces immunoglobulin secreting cells (SCs) also generates HIV-1-specific resting B cells to synthesize antibodies specific to HIV-1. To this end, highly purified B cells from 10 HIV-1-untreated patients were cultured with or without mouse fibroblastic cells expressing the CD40 ligand in the presence of IL-2 and IL-10. The percentage of immunoglobulin SCs we obtained by using the B cell-CD40L stimulation system was equal to 55% to 98% of the circulating memory B cells. Moreover, the anti-HIV-1 IgG, IgA, or IgM antibody SCs represented 1 x 10-2 to 1 x 10-3 of the total immunoglobulin SCs. The anti-HIV-1-specific antibodies detected in cell culture supernatants were directed to gag-, pol-, and env-encoded viral proteins. We found that in AIDS patients, HIV-1-specific resting memory B cells circulate in the blood and can be quantified by their anti-HIV-1 antibody secretion after strong B cell polyclonal stimulation.