Immune responses and resistance to Eimeria acervulina of chickens divergently selected for antibody responses to sheep red blood cells

Resistance to Eimeria acervulina was measured in two lines of chickens that had been divergently selected for high (H line) or low (L line) antibody ( Ab) responses to SRBC, and in a randombred control (C) line originating fro m the same parental stock. Fecal oocyst output of cocks from the three line s from the 17th generation was estimated after primary and secondary infect ion with 2 x 10(5) oocysts. In addition, Ab responses to E. acervulina oocy st antigen and cellular immune responses in vitro to E. acervulina antigen were measured after primary and secondary infection with E. acervulina. No significant line differences were found with respect to fecal oocyst out put after primary infection. Only at the end of the primary infection perio d, i.e., Day 15 postprimary infection, was a significantly lower fecal oocy st out-put found in the H line as compared to the C and L lines. After seco ndary infection, significantly higher fecal oocyst output was found in the C line. Significantly higher Ab response after primary and secondary infect ion were found in the H and C lines as compared to the L line. No line diff erences were found for cellular immune responses to E. aceuvulina oocyst an tigen. These observations imply that selection for enhanced humoral immunity to SR BC did not result in enhanced resistance to E. acervulina in terms of fecal oocyst output. However, the H line might expel E. acervulina more rapidly than the other two lines. The absence of line differences in resistance to Eimeria is discussed with respect to the role of the humoral immune respons e.