Effect of recombinant cytokines on leucocytes and physiological changes in bovine mammary glands during early involution

We examined the effects of administering recombinant bovine cytokines to non-lactating dairy cows and measured mammary gland leucocytes and the involution process. After the final milking, groups of cows were given an intramammary infusion of cytokine in two quarters. These cytokines were recombinant bovine interleukin-2 (rboIL-2) (2*10^5 units, n=6), recombinant bovine granulocyte-macrophage colony stimulating factor (rboGM-CSF) (500 (mu)g, n=4) and recombinant bovine interleukin-1(beta) (rboIL-1(beta)) (10 (mu)g, n=10). Each animal also received an infusion of phosphate-buffered saline (PBS) in the other two quarters as controls. The rboIL-2 and rboGM-CSF were produced in a yeast expression system, while rboIL-1(beta) was produced in Escherichia coli. Leucocyte numbers, bactericidal activity of leucocytes, and concentrations of citrate and lactoferrin in quarter secretion samples were monitored after infusion of cytokine or PBS. Infusion of rboIL-2 had minimal effect on leucocyte numbers and concentrations of citrate and lactoferrin. Both rboGM-CSF and rboIL-1(beta) induced a rapid increase in the number of neutrophils and macrophages compared with control PBS quarters. Concentrations of lactoferrin in secretions were increased by rboGM-CSF and rboIL-1(beta) compared with control PBS quarters. In addition, infusion of glands with rboIL-1(beta) lowered the citrate:lactoferrin molar ratio compared with PBS control quarters. The results indicate that intramammary infusion of either rboGM-CSF or rboIL-1(beta) at cessation of milking immediately increased the number of phagocytic cells in the gland. These cytokines, in particular rboIL-1(beta), also increased the rate of mammary gland involution during the early dry period.