The role of carrageenan in complement activation.

A study has been made of the nature of the interaction between complement and carrageenan, which has been widely reported to inhibit haemolytic complement activity both in vivo and in vitro. Using modified haemolytic complement-fixation tests, the degree of complement consumption by various forms of carrageenan was measured in whole human and rat sera. The median effective concentrations of the carrageenans studied were found to lie in the range 3-300 micrograms/ml for the classical pathway and 500-7800 micrograms/ml for the alternative pathway and were unrelated to sulphate content, as determined by energy dispersive X-ray analysis. It was also found that carrageenan-coated sheep erythrocytes were lysed by complement. This activity was suppressed by ethylene glycol-bis-(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, which inhibits the classical, but not the alternative pathway, providing conclusive evidence that carrageenan preferentially activates the classical pathway. This finding may help in elucidating the inflammatory reaction induced by carrageenan.