Cytokine production and phenotype of Histomonas meleagridis-specific T cells in the chicken

The protozoan parasite Histomonas meleagridis is the causative agent of the re-emerging disease histomonosis of chickens and turkeys. Due to the parasite’s extracellular occurrence, a type-2 differentiation of H. meleagridis-specific T cells has been hypothesized. In contrast, a recent study suggested that IFN-γ mRNA(+) cells are involved in protection against histomonosis. However, the phenotype and cytokine production profile of H. meleagridis-specific T cells still awaits elucidation. In this work, clonal cultures of a virulent monoxenic strain of H. meleagridis were used for infecting chickens to detect IFN-γ protein and IL-13 mRNA by intracellular cytokine staining and PrimeFlow™ RNA Assays, respectively, in CD4(+) and CD8β(+) T cells. Infection was confirmed by characteristic pathological changes in the cecum corresponding with H. meleagridis detection by immunohistochemistry and H. meleagridis-specific antibodies in serum. In splenocytes stimulated either with H. meleagridis antigen or PMA/ionomycin, IFN-γ-producing CD4(+) T cells from infected chickens increased in comparison to cells from non-infected birds 2 weeks and 5 weeks post-infection. Additionally, an increase of IFN-γ-producing CD4(−)CD8β(−) cells upon H. meleagridis antigen and PMA/ionomycin stimulation was detected. Contrariwise, frequencies of IL-13 mRNA-expressing cells were low even after PMA/ionomycin stimulation and mainly had a CD4(−)CD8β(−) phenotype. No clear increase of IL-13(+) cells related to H. meleagridis infection could be found. In summary, these data suggest that H. meleagridis infection induces a type-1 differentiation of CD4(+) T cells but also of non-CD4(+) cells. This phenotype could include γδ T cells, which will be addressed in future studies.