Peripheral blood leucocyte response to coccidial infection: a comparison of the response in rats and chickens and its correlation with resistance to reinfection.

The peripheral blood leucocyte (PBL) response to infection with two species of the intestinal protozoan Eimeria shows a remarkably similar pattern in both rats and chickens. Like resistance to these parasites, the PBL response to reinfection is species-specific and it coincides with the inhibition of development of the parasite and with cellular infiltration of the lamina propria. In primary infections, the numbers of PBL increased biphasically and significant changes were found in the count of polymorphonuclear cells (PMN), lymphocytes, and large mononuclear cells (LMN). A consistent pattern of two increases in PMN, some lymphopenia, and two increases in LMN was found in rats and chickens. The response to secondary infections was more rapid and much briefer, particularly in chickens in which significant changes were detected within hours of infection and consisted of an almost equal increase in PMN and in lymphocytes. This secondary response occurred only in animals challenged with the homologous species. It was not evoked by challenge with a related species which develops in approximately the same area of the intestine.