CHARACTERIZATION OF PHENOTYPE RELATED RESPONSIVENESS OF PERIPHERAL-BLOOD LYMPHOCYTES FROM EIMERIA-TENELLA INFECTED CHICKENS

We have previously shown that the proportion of CD8-expressing T cells (CD8(bright+) and CD4(+) CD8(dim+) cells) in the peripheral blood of chickens increases around 8 days after a primary infection with Eimeri a tenella oocysts. The increase in the CD8(+) eight cells coincides wi th enhanced responses after in vitro stimulation with parasite antigen . In the study described here, the responsiveness of these day 8 PBL w as further characterized by determining their capacity to proliferate and to produce cytokine (IFN-gamma) upon stimulation with E. tenella s porozoite antigen, or non-specific stimuli like T cell growth factor ( TCGF) and anti-CD3 monoclonal antibody (MoAb). Comparirg the responsiv eness of infected responder (day 8) and control chickens, non-specific triggering induced cytokine production in cells from infected animals and proliferation in cells from control animals. When triggered with E. tenella sporozoite antigen, lymphocytes from infected chickens resp onded with proliferation and cytokine production, in contrast to lymph ocytes from control animals that did not respond. The phenotype of the lymphocytes involved in the parasite-specific proliferation and cytok ine production, was characterized in a blocking assay using MoAb direc ted against the CD4 or CD8 molecule. The results suggest that CD8(brig ht+) as well as CD4(+) (CD4(+) CD8(dim+) and possible CD4(+), single p ositive) lymphocytes are responsible for the IFN-gamma production meas ured after stimulation with parasite antigen, whereas the specific pro liferative response appears to be caused by CD4(+) (CD4(+) CD8(dim+) a nd possibly CD4(+), single positive) lymphocytes. We speculate that th e CD8(bright+) cells, present in the circulation around 8 days after a primary E. tenella infection, act as effector cells in protective imm une responses, whereas CD4(+) cells play an important helper function in these responses.