Both interleukin 2 and a second T cell-derived factor in EL-4 supernatant have activity as differentiation factors in IgM synthesis.

Abstract

B cells [from mice] cultured with anti-IgM, BSF-p1 [B cell stimulatory factor p1] and B15-TRF will differentiate into high rate IgM-synthesizing cells in the presence of supernatants from EL-4 cells that have been induced with phorbol myristate acetate. These supernatants contain 2 molecular species (EL-TRF) that have differentiative activity. One co-migrates with interleukin 2 (IL-2) and its activity is blocked by antibody to the IL-2 receptor. Molecularly cloned IL-2, at concentrations of 100 U/ml or more, expresses such EL-TRF activity. The EL-TRF activity of cloned IL-2 can also be inhibited by antibody to the IL-2 receptor. The other material with EL-TRF activity has a MW of .apprx. 32,000. This material lacks IL-2 activity. Antibody to the IL-2 receptor does not impair its function. B cells stimulated with anti-IgM and BSF-p1, with or without B15-TRF, express determinants that react with 2 monoclonal antibodies which recognize distinct epitopes on the T cell IL-2 receptor. These determinants are present at much lower density (.apprx. 100-fold) on stimulated B cells than on HT-2 cells, an IL-2-dependent T cell line. Very small amounts of [3H]IL-2 (< 1,000 molecules per cell) bind to activated B cells. The results indicate that IL-2 binds to a receptor on appropriately prepared B cells and causes them to differentiate into high rate IgM-synthesizing cells.