Increase in specific opsonic activity in bovine milk following experimental Escherichia coli mastitis

An infection in a single bovine mammary quarter with a capsulated Escherichia coli stimulated a long lasting opsonic activity for the phagocytosis and killing of the homologous strain by polymorphonuclear leucocytes. The induced activity was associated with increases in the IgM fraction and an appearance of activity in the IgG2 fraction. The capsular polysaccharide was the major inducing antigen, with the immune whey showing opsonic activity for other strains of E coli with antigenically similar capsules.