Ontogeny of the response of mouse thymocytes to interleukin 1 and interleukin 2

Expression of interleukin-1 receptors in the later period of foetal thymic organ culture and during suspension culture of thymocytes from aged mice

Interleukin-1 has been reported to be involved in thymocyte development by exerting a variety of effects on immature CD4-CD8- double-negative (DN) thymocytes. In contrast to the well-documented involvement of IL-1 in thymocyte development, expression of IL-1 receptors (IL-1R) on thymocytes has not been well demonstrated. In the present study, expression of IL-1R on the developing thymocytes was investigated. Although normal thymocytes barely express IL-1R, expression of IL-1R (type I) substantially increased at days 12-15 of foetal thymic organ culture (FTOC), with an increase of the DN subset. The CD4/CD8 profile of the IL-1R (type I)+ cells showed that these cells were mostly restricted to the DN and CD4+CD8+ subsets. Interestingly, in vitro culture of the thymocytes from an aged mouse, but not those from young adult or newborn mice, revealed similar results to those of FTOC. In addition, half of the IL-1R+ cells that increased in the later period of FTOC were gammadelta thymocytes. These results demonstrate IL-1R expression on thymocytes during ex vivo culture and suggest that IL-1R is expressed in a certain environment during normal thymocyte differentiation.

Characteristics of fetal thymus-derived T cell receptor gamma delta intestinal intraepithelial lymphocytes

We have previously demonstrated that grafting of CBF1 (H-2b/d) fetal thymus (FTG) under the kidney capsule of congenitally athymic nude mice of BALB/c background (H-2d) generates a substantial number of T cell receptor (TCR) gamma delta intestinal intraepithelial lymphocytes (IEL) that were of FTG origin (H-2b+) (see accompanying report). Here we investigated the characteristics of these FTG-derived TCR gamma delta IEL and compared them to the extrathymically derived TCR gamma delta IEL found in nude mice. Phenotypically, FTG-derived TCR gamma delta IEL were similar to their extrathymically derived counterparts in that most were Thy-1-, CD5- and CD8 alpha alpha (homodimer). V gamma and V delta gene usage in thymus-derived and extrathymically derived TCR gamma delta IEL were found to be virtually the same. Functionally, FTG-derived TCR gamma delta IEL were similar to the TCR gamma delta IEL found in euthymic mice as both were relatively anergic to TCR cross-linking in vitro. However, FTG-derived TCR gamma delta IEL differed slightly from extrathymically derived TCR gamma delta IEL, which were completely nonresponsive to the same in vitro stimulation. Overall, these findings support the view that FTG-derived and extrathymically derived TCR gamma delta IEL are almost indistinguishable. Lastly, we demonstrate that despite their thymic origin, development of FTG-derived TCR gamma delta IEL partially takes place extrathymically; that is positive selection of FTG-derived V delta 4 IEL occurs extrathymically. In addition, we demonstrate that the CD8 molecule is not necessary for development and homing of FTG-derived TCR gamma delta IEL. This later finding suggests that the CD8 alpha alpha molecule develops extrathymically for FTG-derived CD8 alpha alpha TCR gamma delta IEL.

Expression and biological activity of interleukin-1 receptors in mouse gamma/delta thymocytes during ontogeny

We have recently shown that the response of mouse thymocytes to interleukin (IL)-1 + IL-2 was maximal at birth and that the responding cells displayed a CD4-CD8- T cell receptor (TcR) gamma/delta + phenotype. Unexpectedly, despite their high proportion of gamma/delta + cells, fetal thymocyte populations responded only weakly to IL-1 + IL-2. In this report, we demonstrate that the discrepancy between the day 17.5 fetal and newborn sensitivities to the combined action of IL-1 and IL-2 is a consequence of the different patterns of high-affinity IL-1 receptor (IL-1R) expression displayed by these two cell subsets. Actually, high- and low-affinity IL-1R are found in TcR gamma/delta + newborn cells and, in contrast, only low-affinity IL-1R are detectable in day 17.5 fetal cells. Our binding and functional studies strongly support the hypothesis that high-affinity IL-1R on the one hand, and low-affinity ones on the other hand, are involved in the response to IL-1 + IL-2 of newborn and day 17.5 fetal thymocytes, respectively. In addition, the high-affinity IL-1R appear to be far more efficient than the low-affinity receptors in promoting IL-2 responsiveness of thymocytes.