Selective suppression of lymphokine production by human hybridoma suppressor factor (HSF)

We have made a human thymus cell hybridoma that secretes an immunosuppressive monoclonal lymphokine, referred to as hybridoma suppressor factor (HSF). This factor modulates the function of CD4+ cells suppressing their IL-2 production and suppressing PWM-induced B cell differentiation into Ig producing cells. Here we have examined the effect of HSF on the generation of T cell-derived lymphokines that regulate B cell growth and differentiation as well as the expression of other proteins involved in the control of T cell growth i.e., the p55 chain of the IL-2R and the transferrin receptor (TFR). HSF suppressed IFN-gamma activity produced by mitogen-stimulated PBMC without affecting the generation of lymphokines responsible for BCGF and BCDF activities. Additionally, HSF did not inhibit the expression of either IL-2R (p55) or TFR by activated T cells in spite of causing the suppression of IL-2 production. This evidence was further supported by experiments in which HSF selectively suppressed the accumulation of IL-2 mRNA without affecting IL-2R (p55) mRNA expression in mitogen-stimulated PBMC. The selective action of HSF may help to clarify the regulatory mechanisms involved in lymphokine gene expression as well as provide a way by which immune responses involved in autoimmunity and transplant rejection may be interrupted.