B-cell stimulation by T-cell-secreted proteoglycan.

We have further characterized a recently described B-cell stimulatory factor that contains chondroitin sulfate proteoglycan and 70- to 75-kDa protein, both of which are secreted by T cells and coisolate (T-cell proteoglycan fraction, T-PGF). Using T-PGF isolated from a T-cell hybridoma (T14), it was observed that the association between B-cell stimulatory activity and CSPG is stable and comigrates on Sephacryl S-200 columns eluted at high salt concentrations (1.5 M NaCl) and on CsCl gradients. The T-PGF stimulated larger numbers of low-density (activated) B cells, but better relative PFC formation occurred in high-density (resting) B-cell fractions. It is proposed that the B-cell stimulatory activity of T-PGF is, in fact, chondroitin sulfate proteoglycan.