Although the production of B cell stimulatory factors by cell lines and hybridomas is well established, production of specific lymphokines by normal T cells in response to antigen stimulation has not been analyzed. We have used bioassays and neutralizing mAbs to demonstrate that IL-2, IL-4, and B cell growth factors (BCGF) are produced during primary and secondary MLRs. IL-2 is detected in the first 12 h of both types of MLR. IL-4 and BCGF appear at 24-48 h in the conditioned medium of the primary MLR, and peak by 12 h in the secondary MLR. The amount of IL-4 in the primary response reaches a level that is 10% of that detected in the secondary. In contrast, BCGF production steadily increases over time in the primary MLR, and maximal production is equivalent to that made in the secondary response. Allogeneic dendritic cells and anti-Ig-activated B blasts both stimulated lymphokine production in the primary MLR, whereas small B cells were weak. In the secondary MLR, all three cell populations stimulated the production of IL-2, IL-4, and BCGF. Therefore, the release of several defined B cell stimulating factors can be detected in the conditioned media of responding primary T lymphocytes.

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