Bactericidal and haemolytic activity of complement in bovine colostrum and serum: effect of proteolytic enzymes and ethylene glycol tetraacetic acid (EGTA).

Bovine colostral whey (CW) possessed heat-labile bactericidal activity against an enteropathogenic serum-susceptible strain of Escherichia coli. Activity was readily destroyed by trypsin or rat pancreatic juice, and less readily by chymotrypsin. Loss of activity due to trypsin, but not by chymotrypsin, could be prevented by addition of excess bovine colostral trypsin inhibitor. A second enteropathogenic strain of E. coli was killed by CW only if exogenous complement was added. This activity was maintained, however, even if the complement was heated 56 degrees C during 15 min. CW possessed only very weak haemolytic activity against sensitised rabbit erythrocytes, but could augment the haemolytic titre of bovine serum and could partially restore haemolytic activity to heat-inactivated bovine serum. These observations indicate that low but significant amounts of complement may occur in bovine colostrum. Sequestration of Ca++ by EGTA abolished all bactericidal and haemolytic activity in CW, and reduced but did not completely abolish these activities in bovine serum or in CW + exogenous complement. The activity of colostral complement therefore appears to be mediated entirely by the classical pathway whereas the alternate pathway may play some part in the bactericidal and haemolytic activities of bovine serum or of CW + exogenous complement.