| Rationale. Eosinophils are "end cell" leucocytes, associated with allergy, asthma and helminthiasis. At sites of inflammation, eosinophils may modulate immune response through expression of the extra-hepatic tryptophan-catabolising enzyme, Indoleamine 2, 3-dioxygenase (IDO). Kynurenines, products of tryptophan cleavage, induce apoptosis of T-cells, including thymocytes. Eosinophils naturally home to the thymi in mammals. Thymus is a primary lymphoid organ, where T-cells develop and undergo selection. My hypothesis is that eosinophils homing to the thymi participate in T-cell development through their expression of IDO. Methods. Immunohistochemistry revealed eosinophils in thymic tissue. Immunocytochemistry and flow cytometry were used to locate IDO protein expression in the thymus particularly in thymic eosinophils. RT-PCR and real-time PCR determined the presence of IDO mRNA in the thymus. Results. Thymic eosinophils express IDO and infiltrate compartments associated with negative selection. The highest IDO transcription correlated with the influx of eosinophils and prevalence of immature thymocytes. |
