Intestinal intraepithelial and splenic natural killer cell responses to eimerian infections in inbred chickens.

Splenic and intestinal natural killer (NK) cell responses were assessed in chickens inoculated with Eimeria parasites. The NK cell activities of both splenic and intestinal intraepithelial lymphocytes (IELs) decreased to a subnormal level during the early phase of eimerian infections but returned to normal or slightly higher than normal levels at about 1 week after the primary inoculation. Lymphocytes obtained from the lamina propria did not show any detectable level of NK cell activity during or following eimerian infections. Significant increases in splenic and intestinal IEL NK cell activities were seen during the early phase of secondary infection. The increase in the IEL NK cell activity that was seen shortly following secondary eimerian infection was accompanied by a substantial increase in the number of IELs expressing the asialo-GM1 antigen. Host strain differences in both splenic and IEL NK cell responses were detected following primary eimerian infections. These results suggest that both splenic and intestinal IEL NK cells may play an important role in the host defense against intestinal protozoan infections.