Effects of chicken thymic stromal cells on the growth and differentiation of thymocytes in vitro

We examined contact-mediated effects of chicken thymic stromal cells (TSC) on thymocyte differentiation by co-cultivation of these cell populations. T he primary cultures of TSC isolated from thymus mainly have consisted of ep ithelial cells which were polygonal in shape, possessed long processes and expressed MHC class II antigen. When thymocytes were co-cultured with TSC, 60% to 70% of thymocytes attached to TSC and some of them engulfed undernea th TSC. These attached thymocytes were CD4(-)CD8(-) and CD4(+)CD8(+) subset s and expressed alpha/beta TCRhigh Or gamma/delta TCRlow. Some of the thymo cytes attaching to TSC showed an increase of intracellular and nuclear dens ity, fragmentation of cytoplasm and nuclei, and DNA fragmentation. And also , thymocytes attaching to TSC contained a higher percentage of cycling (S a nd G(2) + M phase) cells than nonattaching cells. These results indicate th at specific subsets in thymocytes selectively bind to TSC and undergo apopt otic death or proliferation because of interaction with TSC. Chicken TSC ma y play an important role in thymic differentiation by direct contact within the thymus as in mammals. (C) 1999 Elsevier Science B.V. All rights reserv ed.