The in vitro migration pattern of neonatal spleen cells was studied in a system of grafts: the newborn spleen was grafted under the renal capsule of adult mice, either normal, thymectomized as adults, or T-deprived animals. The influence of thymic humoral factors on these cells was studied by grafting some of the hosts with thymic tissue in cell-impermeable diffusion chambers. The results showed that the cells of the neonatal spleen contain subpopulations that migrate specifically to either the thymus, the spleen, or the lymph nodes and that these migration patterns are not influenced by thymic humoral function. In T-deprived animals; however, in the absence of any thymic influences, cells that migrated to the thymus, only, were present. Under the influence of thymic humoral factors, this thymus-seeking population became minimal while a new population of spleen- and nodeseeking cells was detectable. The results provide evidence to suggest that there is a sequence of maturation in terms of lymphoid organ homing of precursor cells and that one population may generate the succeeding populations. There is also evidence to suggest that a thymic humoral factor may play a role in these changes in migration patterns without necessarily direct correlation with changes in classic criteria of T cell maturation.

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This work was supported by Grant INSERM-ATP 56-78-88 and DGRST No 3599.

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