NATURAL HEMOLYTIC AND BACTERICIDAL ACTIVITIES OF SEA BREAM SPARUS-AURATA SERUM ARE EFFECTED BY THE ALTERNATIVE COMPLEMENT PATHWAY

Sea bream serum displayed bactericidal and hemolytic activities. These activities were depleted when serum was incubated with different acti vators of the alternative complement pathway (ACP). Ethylenediaminetet raacetic acid (EDTA) inhibited both the hemolytic and bactericidal act ivities, while ethyleneglycol-bis (B-aminoethyl ether)-N,N,N'-tetraace tic acid (EGTA) was not inhibitory. An antibody against the putative t hird component of sea bream component (C3) was produced. It was observ ed by immunoelectrophoresis that the sea bream C3 and human C3 migrate d in the same position. Crossed immunoelectrophoresis showed that sea bream C3 exhibited a similar pattern of activation when compared with its human counterpart. The anti-sea bream C3 antibody inhibited both b actericidal and hemolytic activities. It was concluded that both serum actions were displayed by the ACP. The best conditions for the sea br eam ACP titration were investigated. Of all mammal erythrocytes tested , rabbit erythrocytes (RaRBC) were found to be the best ACP activators and thus were used for the titration. Sea bream showed very high ACP titers when compared with those of mammals. Absorption of naturally oc curring antibodies against rabbit RaRBC did not influence the ACP tite rs. Enzymatic removal of sialic acid from different mammalian erythroc ytes increased the sensitivity of these cells to hemolysis mediated by the sea bream ACP.