Modification of lymphocyte responsiveness in vitro by lambda carrageenan compared with colloidal silica and depletion of surface adherent cells.

The effects of the immunosuppressive sulphated polygalactan lambda carrageenan on in vitro models of allograft immunity were compared with the effects of removing macrophages (surface adherent and/or phagocytic cells) by established methods. Carrageenan depressed the primary mixed lymphocyte reactions, but not to the same extent as the removal of macrophages. 2-Mercaptoethanol restored the response. Secondary mixed lymphocyte reactions and responses to phytohaemaglutinin were depressed by carrageenan but not by the removal of macrophages, and in these systems 2-mercaptoethanol failed to restore the responses of carrageenan-treated cultures. In contrast, cell-mediated cytolysis by presensitized lymphocytes was not affected by carrageenan or by colloidal silica. Carrageenan depressed cell-mediated cytolysis only if it was present during the sensitization of the effector cells. We conclude that carrageenan can have two dose-related effects in vitro: one on the macrophage and one on the responding lymphocyte.