Peripheral blood white cell responses during concurrent copper deficiency and gastro-intestinal nematodiasis in sheep

Sheep experimentally depleted of copper (Cu) and infected with Trichostrongylus axei and Trichostrongylus colubriformis were studied for changes in white blood cell (WBC) populations, anti-parasite antibody responses and in vitro proliferative response to phytohaemagglutinin (PHA), lipopolysaccharide (LPS) and Trichostrongylus spp. antigens. Increases in circulating total WBC, lymphocyte, monocyte and neutrophil leucocyte numbers had a bimodal distribution which was related to the different developmental stages of the nematode. Eosinophil leucocyte numbers were generally lower than those of uninfected control sheep and could be associated with parasite-induced selective unresponsiveness of PHA responsive cells. The in vitro blastogenic responses of lymphocytes to PHA stimulation increased rapidly soon after infection, reaching a peak at 2 weeks, but then declined rapidly and from 5 weeks after infection responses to PHA were barely detectable. The patterns of proliferative response against LPS and Trichostrongylus spp. antigens were identical and correlated with the appearance of anti-parasite antibodies in the serum. These last three responses reached their maxima 5 weeks after infection and then stabilized at a plateau around peak levels. It was concluded that, although the changes in the host immune response could not be consistently associated with interactions between Cu deficiency and infection, the results nevertheless suggest that Cu, as a micro-nutrient, has a role in the mechanism of cell-mediated immunity in sheep infected with Trichostrongylus spp.