B cell stimulatory factor 1 induces lobster agglutinin 1-separated mouse thymocytes to express cytotoxic T lymphocyte activity.

Mouse thymocytes low in surface sialic acid were prepared by using the lectin lobster agglutinin 1 (LAg1). These LAg1-thymocytes do not become CTL when incubated with Con A or Con A plus mouse rIL-2, whereas unseparated thymocytes and thymocytes with high levels of surface sialic acid develop good levels of polyclonal CTL activity under these conditions. However, LAg1- thymocytes developed high levels of CTL activity when incubated with B cell stimulatory factor-1 (BSF-1), provided as the supernatant of the rBSF-1-secreting T cell hybridoma D9-C1.12.17. Affinity-purified BSF-1 from D9-C1 supernatant and rBSF-1 also stimulated these cells to become CTL, but they were not as active as the D9-C1 supernatant. The ability of D9-C1 supernatant and of affinity-purified BSF-1 to induce CTL activity was inhibited by the anti-BSF-1 mAb 11B11. Moreover, this mAb inhibited the ability of 24-h Con A-stimulated spleen cell supernatant to induce these cells to express CTL activity. 11B11 also inhibited LAg1+ thymocytes from becoming CTL when stimulated with Con A alone. These experiments suggest that BSF-1 is required for LAg1- and LAg1+ thymocytes to become CTL.