Ontogeny of alloreactivity in the chicken as measured by mixed lymphocyte reaction.

Ontogeny of alloreactivity in the chicken thymus and spleen was studied in mixed lymphocyte cultures. Mixed lymphocyte reaction (MLR) to total major histocompatibility complex (MHC) (B-complex in chicken) disparity was first detected in the thymus of 16-day-old embryo and regularly detectable from the 18th embryonal day on. Small strain-specific differences in the strength and appearance of the response were, however, observed. MLR to class I MHC (B-F) antigen disparity was not detectable before hatching. Exogenous interleukin-2-containing supernatant added to the cultures had only a minor effect on MLR of embryonal thymocytes. In the spleen, MLR was first detectable in some strain combinations on day 3 and regularly found on the 7th day posthatching, indicating colonization of peripheral lymphoid organs by thymus-derived mature T cells. Our results show the association of phenotypic and functional maturation of chicken T cells. The ontogeny of alloreactivity can now be compared to the appearance of T cell receptor (TCR), CD4, and CD8-bearing cells in the thymus and peripheral lymphoid organs.