P cell stimulating factor release: a useful assay of T cell activation in vitro.

The coordinate production of multiple lymphokines by activated T cells allows the investigator a choice of assays for antigen recognition in vitro. In this paper, we examine the production of P cell stimulating factor (PSF, a lymphokine identical to interleukin 3) by L3T4+ Lyt-2-T cell clones. PSF production is antigen-specific, Ia-restricted and inhibited by a monoclonal antibody to L3T4, PSF, interferon-gamma (IFN-gamma) and interleukin 2 (IL 2) are all rapidly secreted after antigen or mitogen stimulation. The measurement of PSF avoids problems inherent in the IL 2 and IFN-gamma assays, namely absorption of IL 2 by the producer T cells and failure of the interferon assay to distinguish between interferons of the alpha, beta and gamma classes.