PERIPHERAL-BLOOD LYMPHOCYTES FROM EIMERIA-TENELLA INFECTED CHICKENS PRODUCE GAMMA-INTERFERON AFTER STIMULATION IN-VITRO

Protective immunity to infection by Eimeria parasites has been demonst rated to be dependent on T-cell mediated immune responses and may be a ssociated with the release of cytokines. We have previously shown that the proportion of CD8-expressing T-cells in the peripheral blood of c hickens increases transiently at 8 days after a primary infection with Eimeria tenella oocysts. The increase in the CD8(+) population coinci ded with an increased proliferative lymphocyte response upon stimulati on with E. tenella sporozoite antigen in vitro. In this study, we furt her investigated the functional activity of these peripheral blood leu cocytes (PBL) by determining both the potential to proliferate and to produce IFN upon stimulation with E. tenella sporozoite antigens and m itogens. Enhanced proliferative responses to parasite antigen were acc ompanied by reduced responses to T-cell mitogens around 1 week of infe ction. The IFN activity in the supernatants of the stimulated PBL was measured by the ability to inhibit Semliki Forest Virus (SFV) replicat ion in chicken embryo fibroblasts (CEF) and to activate macrophages, a s measured by nitric oxide production. At eight days after infection t he highest levels of virus inhibition and NO-production were detected upon stimulation with both E.tenella sporozoite antigen and mitogen. A strong correlation between the individual data of the two methods was Sound at this timepoint indicating that the produced cytokine was ind eed IFN-gamma. These results suggest that around eight days after a pr imary E. tenella infection a parasite specific T-cell subset with the capacity to produce IFN(-gamma) is circulating which could be involved in the induction of protective immunity against Eimeria tenella.