T cell mediated polyclonal B cell activation induced by cell-bound fetal calf serum

In vitro exposure of spleen cells to fetal calf serum prior to extensive washing and injection into syngeneic recipients was found to markedly increase in vitro responses to both trinitrophenyl-Ficoll and sheep erythrocytes, increase in vitro spontaneous (background) direct plaque-forming cell responses, and cause a tenfold increase in spontaneous IgM production in vitro. This study demonstrates T cell mediated polyclonal B cell activation which was manifested both in vitro and in vivo.