Frequencies of HIV-reactive B cells in seropositive and seronegative individuals

Peripheral blood mononuclear cells (PBMC) from HIV-infected seropositive (HIV+) but not from normal, seronegative (HIV-) individuals are known to produce anti-HIV antibodies in vitro, in the absence or presence of pokeweed mitogen (PWM). Previous studies showed that up to 20-40% of spontaneously immunoglobulin-secreting B cells from HIV+ individuals are HIV-specific. To analyse the frequency of anti-HIV B cells among 'total' peripheral blood B cells in the present study, we used a limiting dilution assay in which EL-4 thymoma cells induce clones of immunoglobulin-secreting cells in activated as well as resting B cells. Anti-HIV B cells were detected not only in 11/12 HIV+ individuals (with frequencies from 1/910 to 1/21,500 B cells cultured; one negative test was from a person undergoing seroconversion), but also in 4/9 HIV- normal blood donors (1/16,200 to 1/49,000 B cells cultured) and in 3/6 newborns from HIV- mothers (1/11,800 to 1/26,600 B cells cultured). The mean frequency was nine times higher in the HIV+ individuals than in the normal donors. As in previous studies, only the cells from HIV+ individuals generated anti-HIV antibodies in PBMC bulk cultures with or without PWM. The relative proportion of specific anti-HIV antibody/total immunoglobulin in PBMC bulk cultures was 800 times higher by the mean than in EL-4 B cell cultures from HIV+ individuals (whereby the total immunoglobulin secretion for equal numbers of B cells cultured was 500 times lower for PBMC). These different results obtained with different assays suggest that in seropositives most anti-HIV B cells belong to an activated B compartment which is quite small, even in a disease with B cell hyperactivity. Therefore, the specific B cells are strongly diluted among the EL-4 cell-responsive, total B cells. On the other hand, the EL-4 assay can detect HIV-reactive B cells in the B cell repertoire of normal, non-infected individuals.