Function of bovine blood and mammary gland mononuclear cells during the nonlactating period

Bovine mammary mononuclear cells have been shown previously to be hyporesponsive in various functional assays compared to blood mononuclear cells. Mammary mononuclear cell hyporesponsiveness may contribute to susceptibility of the bovine mammary gland to intramammary infection, particularly during physiological transitions of the gland when susceptibility to infection is highest. Therefore, experiments were conducted to determine whether mammary mononuclear cell hyporesponsiveness in proliferative assays was reversible in vitro, and to evaluate potential methods of overcoming hypo responsiveness. Production of interleukin—2 by mammary mononuclear cells was evaluated also to determine if hyporesponsiveness in proliferative assays was due to lack of secretion of interleukin-2. Addition of autologous heat-inactivated serum to bovine mammary mononuclear cells in culture enhanced proliferation of these cells in response to mitogenic lectins and allogeneic cells markedly. In particular, proliferative responses of mammary mononuclear cells isolated during physiological transitions of the gland could be enhanced by addition of serum.

Ability of recombinant bovine interleukin-1β and interleukin-2, which are critical components in mononuclear cell proliferation, to enhance mammary mononuclear cell proliferation was evaluated. Recombinant interleukin-1β was ineffective in enhancing blood or mammary mononuclear cell proliferation in the presence or absence of suboptimal concentrations of mitogens. In contrast, recombinant interleukin-2 enhanced blood and mammary mononuclear cell proliferation markedly in the presence and absence of suboptimal concentrations of mitogens, including proliferation of cells isolated during physiological transitions of the mammary gland. Mammary mononuclear cell response to optimal concentrations of mitogens was comparable to that of blood mononuclear cells, possibly due to addition of 2-mercaptoethanol to culture media. Production of interleukin~2 by mammary mononuclear cells was comparable to blood mononuclear cells. Data presented in these studies suggest that previously reported mammary mononuclear cell hyporesponsiveness may have partially been due to suboptimal culture conditions, and that based upon proliferative capacity and production of interleukin-2 bovine mammary mononuclear cells may be comparable to blood mononuclear cells. Consequently, enhancement of mammary mononuclear cells in vivo to combat intramammary infections may be feasible. Data presented herein further suggest that recombinant bovine interleukin-2 may be effective as an immunoenhancer of bovine mammary mononuclear cells.