MONOCLONAL-ANTIBODY TO A THY-1 RELATED ASSOCIATED MOLECULE IDENTIFIESA SUBPOPULATION OF IMMATURE MOUSE THYMOCYTES/

In this study, NMT-1 mAbs have been shown to identify a thymocyte cell surface molecule (Immature Thymocyte Marker-1, ITM-1) expressed on 86 .2 to 90.8% of CD4(+)CD8(+)CD3(-/lo/int) cells within the thymus of Ba lb/c, CBA, C57B1/6, 129 Rej, A/J and AKR mice. Similarly, immunoprecip itation analysis of cell membrane extracts from (125)Iodine-labelled t hymocytes, using NMT-1mAbs, identified 14.5 and 18.3 kDa molecules fro m all strains of mice examined. Comparison of these immunoprecipitatio n profiles with those produced by rat IgG(2b) anti-Thy-1 antibodies in dicated that NMT-1 mAbs recognized a subspecies of the Thy-1 molecule. Unlike the Thy-1 molecule, the expression of ITM-1 molecules in Balb/ c, CBA, C57B1/6, 129Rej, A/J and AKR strains of mice was restricted to the thymus. The ITM-1 molecule was not expressed on lymphoid cells wi thin the spleen, lymph node, bone marrow, peritoneal cavity and periph eral blood in these strains. Phenotypic characterization associated th e expression of ITM-1 molecule with the CD4(+)CD8(+)CD3(-/lo/int) thym ocyte subpopulation indicating that NMT-1 mAbs recognize an epitope on a distinct developmentally-related Thy-1 glycoform. The expression of the ITM-1 molecule on differentiating thymocytes may prove useful in further subdividing immature thymic subpopulations, particularly those implicated in positive and negative selection.