Activated B cells can deliver help for the in vitro generation of antiviral cytotoxic T cells.

The experiments described in this paper show that activated B cells can deliver help for antiviral cytotoxic T (Tc) cell responses in vitro. This conclusion is based on four observations. (i) Influenza viruses induced secondary Tc cell responses in vitro in the absence of CD4+ T cells. This capacity correlated with the B-cell mitogenicity of these viruses. (ii) Depletion of both CD4+ T cells and B cells prevented the generation of anti-influenza Tc cell responses, whereas depletion of either CD4+ T cells or B cells alone failed to do so. In addition, supplementation of unprimed B cells restored the Tc cell responsiveness of primed splenocytes that had been depleted of both CD4+ T cells and B cells. (iii) Contact between T and B cells was not obligatory for the delivery of B-cell helper signal, and hence help was mediated by a soluble factor(s). (iv) Lipopolysaccharide-activated B cells could replace the CD4+ T-cell requirement in the induction of Tc cell responses to nonmitogenic influenza virus in vitro.