The immune system on the ruminant mammary gland and its role in the control of mastitis.

Immunoglobulins in mammary secretion are derived from blood serum or are made locally by cells of the lymphocyte-plasma cell series situated close to the glandular epithelium. The major immunoglobulin in colostrum and milk of ruminants, IgG1, is derived from the blood and is transferred into secretion selectively relative to IgG2, probably by a mechanism requiring specific receptor sites on the basal of intercellular membrane of the glandular epithelium. Acute inflammation causes suppression of selective transfer of IgG1, but there is a marked increase in the transfer of proteins, such as IgG2 and serum albumin, which enter secretion nonselectively. Infusion of antigen into the mammary gland of ruminants some weeks before parturition induces a persisting local production of antibody, most of which is associated with IgA and IgM. IgA cells in the mammary gland probably originate in the intestine, and prior antigenic stimulation of the gut may be required for maximal IgA antibody responses in the gland. Local immunization with staphylococcal vaccines gives a measurable degree of protection against staphylococcal challenge. Systemic immunization with viable staphylococci leading to subcutaneous abscess formation elicits significant protection to subsequent mammary challenge which is attributable, at least in part, to specific antibody of the IgG2 class cytophilic to polymorphs.