The inflammatory activity of activated complement in ovine and bovine mammary glands

Infusion of zymosan-activated plasma (ZAP), a source of activated complement, induced inflammation in non-lactating mammary glands but not in lactating glands of ewes and cows. Interstitial injection of ZAP in lactating ovine glands also failed to induce inflammation as assessed by the neutrophil content of milk. The inflammatory activity of ZAP in non-lactating glands was inhibited by infusion of whole milk but not by skimmed milk. These results suggest that components of whole milk mask the inflammatory activity of activated complement. In addition, lactating mammary tissue of ewes and cows may lack sensitivity to the inflammatory effect of activated complement. Thus, activated complement cannot be an important mediator of inflammation in the lactating gland.