Characterization and cDNA cloning of a novel murine T cell surface antigen YE1/48

T cell surface antigens are thought to play significant roles in immunological functions. They are involved in cellular interactions and T cell activation and proliferation. Characterization of T cell antigens is important in understanding the molecular machanisms underlying immune responses. The subject of this thesis is to characterize a novel murine T cell surface antigen called YE1/48. YE1/48, defined by two rat monoclonal antibodies YE1/48.10.6 and YE1/32.8.5, is a dimeric glycoprotein with molecular size and charge resembling the murine T cell antigen receptor α/β. It was initially detected at high levels on two T cell lymphomas, EL-4 and MBL-2. In my thesis studies, the YE1/48 antigen was characterized biochemically, a cDNA clone was isolated, and its expression in lymphoid cell populations was determined. The YE1/48 antigen was found to be distinct from the T cell receptor based on direct comparisons of their primary sequences as well as immunological analyses. It is likely a homodimer with similar or identical subunits. No homology with any known proteins could be detected, including the human T cell activation antigen CD28 (T44) which also has a similar dimeric structure as YE1/48. No function of the YE1/48 antigen could be derived from its primary sequence or with the use of the two monoclonal antibodies because the antibodies do not appear to bind to the surface of intact normal T lymphocytes. Some intriguing characteristics of the YE1/48 antigen were observed in the current studies. The YE1/48 antigen belongs to a rare group of type II membrane proteins with orientation of the amino-terminus inside the cell and the carboxy-terminus outside. The YE1/48 gene may have two alleles among different mouse strains and may belong to a multigene family. YE1/48 is expressed at low levels on a wide range of T cells with no restriction to their differentiation stages, and on spleen B cells as well as bone marrow cells. Its expression on lymphocytes is not related to activation or proliferation. However, YE1/48 expression appears to be induced at high levels by Abelson Murine Leukemia Virus-transformation of pre-B cells. Moreover, the epitopes defined by the YE1/48.10.6 and YE1.32.8.5 antibodies seem to be exposed only on three T lymphomas but not on normal T cells. It is thus tantalizing to speculate a correlation of the high level expression of YE1/48 antigen and its epitope exposure on transformed lymphocytes with cellular transformation. In summary, YE1/48 was found to be a novel T cell surface antigen which has similar dimeric structure as the murine T cell receptor α/β and human CD28 (T44). It has now been characterized biochemically, molecularly cloned, and its expression on lymphoid cells has been determined. Although the function of YE1/48 antigen remains unknown, a number of intriguing characteristics observed in the current studies have certainly called for further studies on the antigen and the determination of its function.Science, Faculty ofMicrobiology and Immunology, Department ofGraduat