Suppression of mitogenic response of peripheral blood mononuclear cells by bovine mammary secretions.

Effects of bovine mammary secretions collected at different stages of the lactation cycle on blood mononuclear cell response to mitogens were evaluated. Mammary secretion skims and wheys collected 7 and 28 d following cessation of milking, at parturition, and during early lactation were used. Colostrum and mammary secretions obtained 7 d after milk cessation were associated with greatest inhibition of mononuclear cell blastogenesis. Milk collected during early lactation caused the least inhibition. Mammary secretion wheys caused greater inhibition of blastogenesis than skims. Dilution of mammary secretions reduced blastogenic inhibition. Phytohemagglutinin-stimulated mononuclear cells were less inhibited by mammary secretion than Concanavalin A-stimulated cells. Suppression of mononuclear cell activity, particularly during early involution and at parturition, may influence susceptibility of the bovine mammary gland to new intramammary infections during physiological transitions of the udder.