Immunosuppressive activity of carrageenan for cell-mediated responses in the mouse

Unfractionated carrageenan was highly toxic to CBA mice. By using moderately nontoxic regimens, the immunosuppressive properties of carrageenan were examined in several assays. The growth of tumour allografts was only modestly enhanced at low dosages, but dramatic enhance ment of tumour growth and feeble prolongation of skip allograft survival occurred only at a very high dose. Mixed lymphocyte culture reactivity was significantly diminished at both high and low doses. Phytohaemagglutinin responsiveness was suppressed in the spleen but not in the mesenteric lymph node cells. Changes in the ability of normal syngeneic lymphoid cells to "home" to the lymphoid organs of treated mice were confined to the period immediately after carrageenan administration, an observation that was not temporally related to the suppressive action of carrageenan. It is concluded that, compared with its effect on antibody formation, carrageenan is a very poor inhibitor of cell-mediated responses. Possible reasons for this are discussed.