The glycolipid asialo GM1 as a new differentiation antigen of fetal thymocytes.

Antibody directed to the neutral glycolipid "asialo GM1" was found to react with the majority of thymus lymphoid cells lacking characteristic T cell markers in mice at an early embryonic stage (13 days of gestation). The proportion of these asialo GM1-positive cells (asialo GM1+ cells) decreased strikingly thereafter, contrasting with an increased fraction of lymphocytes possessing T cell surface markers such as Thy-1, Lyt-1, and Lyt-2. After about 18 gestational days, only a few asialo GM1+ cells were detected in the thymus as well as in other lymphoid organs. Double-staining analysis of the embryonic thymocytes (13 days of gestation) with anti-asialo GM1 and anti-Thy-1 demonstrated that thymocytes stained with anti-asialo GM1 did not react with anti-Thy-1, and vice versa. Morphologic examination by immunoelectronmicroscopy demonstrated that these asialo GM1+ cells were mainly composed of immature, large lymphoid cells having large nucleoli and relatively abundant cytoplasm with many polysomes. These results suggest that asialo GM1 is present on very early thymocytes and is lost as the mature murine T cell protein antigens Thy-1, Lyt-1, and Lyt-2 develop on these cells. The antibody to this glycolipid is a useful tool for studying embryonic thymic differentiation.