Identification of Chicken GITR and GITR Ligand, Proof of Their Mutual Interaction, and Analysis of Chicken GITR Tissue Distribution by a Novel Antibody That Reveals Expression on Activated T Cells and Erythrocytes

Glucocorticoid-induced TNFR (GITR) and its ligand, GITRL, belong to the costimulatory members of the TNF superfamily and are crucially involved in the formation and modulation of an effective immune response, comprising innate as well as adaptive mechanisms. In this study, we identify and describe chicken GITR and GITRL, and provide an initial characterization of the newly developed chGITR-specific mAb 9C5. Structural analyses of the putative chicken molecules GITR and GITRL confirmed the conservation of classic topological features compared with their mammalian homologs and suggested the ability of mutual interaction, which was verified via flow cytometry. Whereas only minute populations of native lymphocytes isolated from spleen, bursa, and thymus expressed GITR, it was strongly upregulated upon activation on αβ and γδ T cells, comprising CD4 + as well as CD8 + subsets. In blood, a fraction of CD4 + CD25 + T cells constitutively expressed GITR. In addition, virtually all chicken erythrocytes displayed high levels of GITR. Our results verify the existence of both GITR and its ligand, GITRL, in chickens; they provide the basis and novel tools to further characterize their impact within the immune response and reveal the so-far unrecognized expression of GITR on erythrocytes.