Vaccination-induced activation of human blood T cells suppressing pneumococcal polysaccharide-specific B cells

In order to study the regulation of the human B cell response to pneumococcal polysaccharides (PPS), anti-PPS-secreting cells (SC) and Ig-SC were quantitated in unstimulated and EBV-stimulated cultures of blood mononuclear cells (MNC) established before and one and two weeks after vaccination. In unstimulated cultures established one week after vaccination, significant numbers of anti-PPS-SC were detected; however, they were observed only in cultures depleted of T cells (mean: 62/106), suggesting the presence of T cells suppressing in vivo-activated PPS-specific B cells. In EBV-stimulated cultures depleted of T cells, low numbers of anti-PPS-SC were observed before the vaccination, and the numbers of these cells increased significantly two weeks after the immunization (from 28 to 48/106). In contrast, the numbers of anti-PPS-SC and total Ig-SC decreased in EBV-stimulated cultures of unseparated MNC established after the vaccination, suggesting T cell-mediated suppression. The findings were not explained by changes in the numbers of blood T helper (Leu 3+) or T suppressor (Leu 2+) cells following the vaccination. Possibly the vaccination induces the appearance in the blood of activated suppressor cells responsible for the suppression of B cells in unstimulated and EBV-stimulated cultures.