Lactate dehydrogenase A-dependent surface expression of immature thymocyte antigen-1: An implication for a novel trafficking function of lactate dehydrogenase-A during T cell development

A possible involvement of lactate dehydrogenase A (LDHA) in the translocation of a thymic differentiation antigen, immature thymocyte antigen-1 (IMT-1), from cytoplasm to cell surface membrane during thymocyte differentiation is described. Transfection of cDNA for LDHA, but not LDHB, into EL4 cells, which expressed IMT-1 in the cytoplasm but not on the cell surface, induced the expression of IMT-1 on the cell surface. This translocation process seemed to be dependent on the translation of LDHA cDNA in EL4 cells, as well as the native structure of LDHA composing of coenzyme binding domain, catalysis domain, and subunit contact domain. Immunoprecipitation analysis revealed that LDHA could be co-precipitated with IMT-1 from the cell surface of EL4 cells that had been transfected with LDHA cDNA, suggesting that some of LDHA is associated with cell surface IMT-1 on the transfectants. Flow cytometry analysis of thymocyte subpopulations showed that some thymocytes at the CD4^-CD8^- double negative stage express both IMT-1 and LDHA on their surface. These data indicate that LDHA, in addition to its function in the metabolism in the glycolytic pathway, may have a novel function in the expression of a cell surface antigen during T cell development.