Characterization of a serum inhibitor of MLC reactions: II. Molecular structure and dissociation of inhibition against responder and stimulator function

Abstract

Any factor that inhibits mixed leukocyte cultures (MLC) by mechanisms other than destroying the responding cells provides us with a tool for analyzing how histoincompatibility is recognized and translated in vitro into a positive lymphocyte response. Sera from multiparous women often contain such inhibitory factors. We have been characterizing such a serum, JH, and find that the inhibitory activity is associated with the 7S IgG 1, G 2, or G 4 fraction. The serum can inhibit lymphocytes either as responding or stimulating cells. A new approach to studying this phenomenon is described in which cells are first preincubated with either JH or AB serum, washed thrice and added to MLC. With this technique, responder and stimulator functions of some persons' lymphocytes can be dissociated. This adds a new dimension to the assessment of leukocyte histocompatibility by MLC and strongly suggests the existence of more than one type of inhibitory antibody in JH serum. Inhibition by the serum can be abrogated by an additional preincubation of inhibitor-coated responder cells with antihuman light chain serum. The theoretical implications of these results are discussed.