Dendritic cell-B-cell interaction: dendritic cells provide B cells with CD40-independent proliferation signals and CD40-dependent survival signals

Abstract

Dendritic cells (DC) have recently been shown to play an important role in B-cell function. We have previously shown that DC can capture and retain unprocessed antigen in vitro and in vivo, and can transfer this antigen to naive B cells to initiate antigen-specific antibody responses. We also demonstrated that DC were providing B cells with isotype-switch signals independent of T cells but that T-cell help was essential for antibody production. In this study, using B cells and DC from wild type (WT) and CD40 knockout (CD40KO) mice we show that DC initiate proliferation of B cells independently of CD40, because WT or CD40KO DC could induce proliferation of WT or CD40KO B cells, but proliferation was greater in the absence of CD40. DC also provide B cells with survival signals as WT DC improved viability of B cells after a 5-day culture but survival was reduced in the absence of CD40 expression.

Figure 1

Proliferation of Wild type (WT) and CD40 knockout (CD40KO) B cells cultured with WT and CD40KO DC for (a) 24 hr and (b) 3 days. Purified, irradiated DC and purified B cells were cultured at a ratio of 10 B cells to 1 DC. The cells were cultured in 96-well, round-bottomed plates for the required period, 1 μCi [³H]TdR added and cells harvested after 18 hr.

Figure 2

Flow cytometry profiles of WT and CD40KO B cells either unstimulated or cultured with DC. Purified DC and B cells were cultured for 5 days and then treated with fluorescein isothiocyanate (FITC)–B220 and 7AAD to measure viability. The histograms show 7AAD exclusion of B220-expressing cells.