Carrageenan: a review of its effects on the immune system.

Carrageenans (kappa, lambda and iota) are sulphated polysaccharides isolated from marine algae that can markedly suppress immune responses both in vivo and in vitro. Impairment of complement activity and humoral responses to T-dependent antigens, depression of cell-mediated immunity, prolongation of graft survival and potentiation of tumour growth by carrageenans have been reported. The mechanism responsible for carrageenan-induced immune suppression is believed to be its selective cytopathic effect on macrophages. This property of carrageenan has led to its adoption as a tool for analysing the role of these cells in the induction and expression of immune reactivity. Systemic administration of carrageenan may, however, induce disseminated intravascular coagulation and inflict damage on both the liver and kidney. This is an important consideration in the interpretation of the effects of carrageenan in vivo and precludes its use as a clinical immune suppressant.