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Characterization of Activities Inducing Polyclonal Maturation of Activated B Lymphocytes to Immunoglobulin Secretion

Supernatants from long‐term in vitro‐propagated helper T‐cell clones were analysed for their ability to induce polyclonal maturation of B lymphocytes under conditions that ensured activation and proliferation of the target cells. In gel filtration analysis, three peaks of activity appeared corresponding to molecular weights of about 100 kD, 60 kD, and 30 kD. When the same supernatants were run on sodium dodecyl sulphate gels under reducing conditions, only the last two peaks of activity could be detected. Flat‐bed isoelectric focusing gave two peaks of activity corresponding to isoelectric points of pH 5–6 and pH 8–9. These peaks of activity were devoid of any activity supporting proliferation of either T or B cells, and they induced the expression of several heavy‐chain isotypes. Furthermore, when the same analysis was performed on the B‐cell line WEHI 279.1, only one peak was obtained (molecular weight of about 60 kD; isoelectric point, approximately pH5–6), a result suggesting alternate pathways of induction of B cells to high‐rate secretion cells.