Comparison of immune responses in inbred lines of chickens toEimeria maximaandEimeria tenella

SUMMARYImmune responses of 4 inbred lines of chickens, that differ in resistance toEimeria maximaandE. tenella, were examined. Significant differences were found inin vitroproliferation of peripheral blood lymphocytes toE. maximasporozoite antigen, the more resistant lines C and 72having higher responses than the more susceptible line 151. These differences existed pre-infection and were enhanced following both primary and a second infection. The proportions of lymphocyte subsets in the peripheral blood following primary infection also differed between lines, with significantly higher percentages of CD8 + and TCR1 + lymphocytes circulating in the more resistant birds. In contrast, there were few differences between lines in either resistance or inin vitroproliferation of peripheral blood lymphocytes toE. tenellasporozoite antigen either pre-infection or following a primary infection. However, after a second infection when there were significant differences in resistance between lines, as measured by oocyst excretion, there were also significant differences in lymphoproliferation with the more resistant lines 151 and 62having higher responses than the more susceptible line C. Thus forE. maximathere is a direct relationship between resistance to infection and lymphoproliferation in response to parasite antigen. This implies that differences in cellular immunity may account for differences in resistance between lines, and since these specific responses are enhanced by infection they may also reflect important immune mechanisms. For the rather less immunogenicE. tenella, the correlation between resistance and lymphoproliferation is not so clear. However, where there were significant differences between lines, i.e. after a second infection, the direct relationship between resistance and lymphoproliferation was upheld.