Systemic and local mammary gland immunity to udder infection in goats by various Staphylococcus species

Abstract The objective of the present study of the goat mammary-gland defense system was to characterize and compare the immune responses – locally in the mammary gland and systemically in the blood – to intramammary infection with various staphylococci. In all cases the SCC and total leukocyte counts were significantly higher in the infected than in uninfected glands, the highest being in milk from glands infected with Staphylococcus aureus . Leukocyte distributions in the milk showed significant differences among groups, only in the percentage of PMN, with no differences in percentages of T (CD4 + and CD8 + ) lymphocytes and macrophages. The numbers of B cells bearing CD21 were negligible in all milk samples. In blood, no differences were found in numbers and distributions of erythrocytes and white blood cells. All infected goats were seropositive to homologous bacteria, with high mutual cross-reactivity whereas uninfected goats were seronegative. In vitro bacterial phagocytosis of cells from blood of uninfected goats found differing dynamics among the various staphylococci, and addition of bacterial exosecretions had no effect. In contrast, when the same assays were conducted with blood cells from infected goats, phagocytosis was faster in homologues than in heterologues and exhibited different dynamics. Bacterial exosecretions, both homologous and heterologous, decreased the rate and percentage of active PMN in contrast to cells from uninfected goats. The present results suggest that the host immunity to the various staphylococci is similar, and that it involves systemic immunity, but does not eradicate the bacteria. This suggests that during evolution, similar IMI-causing bacteria attained a balance with the host, through which the host maintained its overall performance while allowing the bacteria to survive.