Characterization of stromal cell populations in the developing thymus of normal and nude mice.

The role of the thymic stromal components in T cell maturation has been investigated by compairing stromal composition in the developing thymus of normal mice with that of nude mice which are unable to support thymopoiesis. Stromal cell populations have been characterized using monoclonal antibody recognizing class II (Ia) major histocompatibility complex antigens, monoclonal antibody A2B5 recognizing GQ gangliosides characteristic of neuroendocrine cells and monoclonal antibody LE.61 recognizing a determinant associated with the tonofilaments of simple epithelia. Using these probes we have shown that the majority population of Ia+, LE.61+ cells is distinct from the A2B5+ stromal population and that both these populations appear early in normal thymus development showing a similar pattern in vivo and in thymus lobes developing in organ culture. In the nude thymic rudiment both Ia and LE.61 labeling are absent supporting previous conclusions on the epithelial nature of the thymic defect in these animals. In contrast, A2B5+ cells are present in the nude thymic rudiment indicating that these cells are unlikely to share the same developmental origin as the Ia+ epithelial population. In functional terms these results suggest that the Ia+ LE.61+ components, deficient in the nude mouse, are essential for normal thymus function and that whatever the function of the A2B5+ population, alone they are not sufficient to support thymocyte development.