The structure and function of beta TCR on immature thymocytes.

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Recently it has been shown that the expression of betaTCR is an important step in the differentiation of CD4^-8^- thymocytes into CD4^+8^+ cells ant that the betaTCR chain is expressed on immature thymocytes in the absence of other TCR chains.In order to study the structure of the immature betaTCR complex and its function in thymocyte differentiation,a thymic lymphoma cell line (LSB11-1)was established.LSB11-1 cells express betaTCR on the cell surface but few CD3.Also in this cell line,betaTCR is not associated with alphaTCR.alphaTCR-gene-transfectant of LSB11-1 cells,LSB11-1alpha29, express alphabetaTCR with CD3 complex on the cell surface.Recently it has been shown that IgD molecules could be expressed on the cell surface in the absence of mbl molecules which correspond to CD3 in B cells,and that those IgD molecules are linked with glycosylphosphatidylinositol(GPI). Treatment of LSB11-1 cells with phosphatidylinositol specific phospholipase C(PI-PLC)reduced the expression of betaTCR on LSB11-1 cells,indicating that the betaTCR is GPI-linked,although the expression of alphabetaTCR on LSB11-1alpha29 cells was not changed by PI-PLC treatment.Cell surface expression of GPI-linked betaTCR was also found on CD3^-,betaTCR^+ thymocytes in betaTCR transgenic mice.However CD3^<high>,betaTCR^<high> mature thymocytes did not express GPI-linked betaTCR on the cell surface,indicating that immature thymocytes can express the GPI-linked betaTCR.Although a transient increase in cytoplasmic CA^<2+> was observed when LSB11-1alpha29 cells were stimulated with betaTCR antibodies or CD3 antibodies,cytoplasmic CA^<2+> increase in LSB11-1 cells was not found when stimulated with those antibodies.Presently we are investigating what kind of signal is transduced via the immature betaTCR complex.These results should show the role of immature betaTCR complex in differentiation of immature thymocytes.