A human soluble suppressor factor affecting lymphocyte responses in vitro.

Abstract

A soluble suppressor factor (SSF) which exhibits suppressive activity toward the proliferative response of normal lymphocytes to concanavalin A, alloantigens in mixed lymphocyte culture (MLC), and toward pokeweed mitogen-stimulated Ig synthesis and secretion in vitro was revealed in the supernatant of normal human peripheral blood lymphocyte cultures. Suppression of the proliferative response in MLC reached maximal levels when added SSF-containing supernatant approximated 20% by volume of the culture medium. Suppression in the MLC acted at the proliferative stage. SSF acts independently of cytotoxicity and is stable at 56.degree. C for 30 min, but is inactivated at higher temperatures. Addition of SSF to the MLC as late as day 4 after initiation of the culture results in suppression of transformation. This factor(s) may regulate the magnitude of several immune responses in humans.