Mechanisms of Transfer of Immunoglobulins Into Mammary Secretion of Ewes

Summary The primary purpose of this paper was to determine whether selective transfer of IgA and IgM is effected by the glandular epithelium of the mammary gland in a manner similar to that for serum derived IgG1. Concentrations of IgG1, IgG2, IgA, IgM and albumin were measured in blood, mammary lymph and milk collected from 8 lactating ewes which had been infused with antigen in one of the pair of mammary glands 3 weeks prior to parturition. Although the concentrations of IgG1, IgG2, and albumin in whey from infused glands were not significantly different from the concentrations of comparable, proteins in whey from non‐infused glands, concentrations of IgA and IgM were respectively 3 and 2 limes higher (P < 0.05) in whey from infused glands. Anti‐body titres were 40‐50 times higher in whey from infused than non‐infused glands. The mean whey:lymph ratios for IgA and IgM were 3‐4 times higher for infused than non‐infused glands. Comparable ratios for IgG2 and albumin were much lower than those for IgA and IgM; values for IgG2 were 30‐80 times less than for IgA and 3‐5 times less than for IgM. Whey:lymph ratios for IgA and IgM for non‐infused glands of 2 of the ewes, in which there was negligible local production of IgA and IgM, were actually less than those for IgG2. The results showed that the magnitude of preferential transfer of IgA and IgM was related to the activity of the local immune system. It is suggested that local production of IgA and IgM by plasma cells which are located in close association with the glandular epithelium, creates a concentration gradient with the highest concentration immediately adjacent to the basal membrane of the epithelial cells. In this situation preferential transfer of IgA and IgM across the glandular epithelium could occur, without the necessity for specific receptor sites as postulated for selective transfer of IgG1.