Carrageenan-induced suppression of T-lymphocyte proliferation in the rat: abrogation of suppressor factor production by the prostaglandin synthesis inhibitors, indomethacin and ETYA.

Carrageenan, an algal polygalactan reputed to be selectively toxic for macrophages, is widely employed as a tool to dissect pathways of cell-mediated immunity. In the present study, corn oil-elicited rat peritoneal macrophages after 72 h culture with 10 micrograms/ml Seakem 9 Carrageenan secreted a soluble suppressor factor capable of abrogating T-cell activation by phytohemagglutinin-P (PHA). Addition of the prostaglandin synthesis inhibitors Indomethacin or 5,8,11,14-eicosatetraynoic acid (ETYA) prevented inhibitor synthesis by Carrageenan-conditioned macrophages. Seakem 9 and lambda Carrageenans added directly into spleen cell cultures failed to diminish lymphocyte proliferation, but rather stimulated spleen cell division. Macrophages cultured with low concentrations of Carrageenan appeared to be activated on the basis of enhanced tumoristatic capacity against Schmidt-Ruppin sarcoma cells. Thus, macrophages activated by low concentrations of Carrageenan in vitro appear to secrete a product of arachidonic acid metabolism which is a potent inhibitor of PHA-induced spleen cell mitogenesis.