Regulatory mast cells. I Suppressive action of their products on an in vitro primary immune reaction.

Products of mast cell degranulation, as well as histamine and serotonin, were added to a Mishell and Dutton preparation for in vitro primary immunisation (induction of IgM antibody formation) to sheep or horse red blood cells. Degranulation products were either obatined beforehand by reacting passively sensitised mast cells with the corresponding antigen (unrelated to or identical with the in vitro immunising antigen) or liberated into the culture medium where mast cells actively sensitised to the in vitro immunising antigen had been added. A 46 to 72 % reduction of direct (IgM) plaque forming cells was observed in all cases. This reduction was prevented by anti-histamine. The responsible mediators were active in the 0 to 24 hour period after antigen introduction. The anaphylactic degranulating antibodies triggering this inhibitory activity were found to be thermolabile in one experiment. An in vivo-induced mast cell degranulation led to a reduced formation of plaque forming cells. The enhancing and immunoregulatory activity of anaphylactic mouse antibodies is therefore tentatively and at least partially attributed to their capacity to degranulate mast cells after contact with the antigen.