T lymphocyte roles during Eimeria acervulina and Eimeria tenella infections

This study evaluated the effects of selective depletion of T lymphocytes on Eimeria infections in chickens. Cell depletions were initiated in day- or week-old Hyline SC strain chickens using intra-peritoneal injections of monoclonal antibodies to CD4, CD8, or T cell receptor (TCR) alpha/beta. Control chickens received injections of irrelevant monoclonal antibody or phosphate buffered saline (PBS). Following the establishment of cell depletion, chickens were infected orally with E. acervulina or E. tenella, 1 x 10(4) oocysts for primary infections and 2 x 10(5) oocysts for secondary infections. Chickens treated with anti CD4 monoclonal antibody produced significantly more oocysts than controls following primary E. tenella but not E. acervulina infections. Development of resistance to challenge infection was unaffected. These results suggest that CD4(+) lymphocytes are important in controlling primary infection with E. tenella. Chickens treated with anti-CD8 or anti-TCR alpha/beta monoclonal antibodies produced significantly fewer oocysts than controls following primary infection but significantly more oocysts than controls following secondary infection with both E. tenella and E. acervulina. Additionally, anti-CD8 treatment abrogated resistance to challenge infection. CD8-depleted chickens may exhibit decreased oocyst production following primary infection due to a lack of CD8(+) lymphocytes to serve as transporting cells for sporozoites. The abrogation of resistance to secondary infection in CD8- and TCR alpha/beta-depleted chickens suggests that these cells are necessary for the development of protective immunity to coccidia.