Monoclonal antibody to a Thy-1 related/associated molecule identifies a 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 Balb/c, CBA, C57B1/6, 129 Rej, A/J and AKR mice. Similarly, immunoprecipitation analysis of cell membrane extracts from 125Iodine-labelled thymocytes, using NMT-1mAbs, identified 14.5 and 18.3 kDa molecules from all strains of mice examined. Comparison of these immunoprecipitation profiles with those produced by rat IgG2b anti-Thy-1 antibodies indicated 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 within the spleen, lymph node, bone marrow, peritoneal cavity and peripheral blood in these strains. Phenotypic characterization associated the expression of ITM-1 molecule with the CD4+CD8+CD3-/lo/int thymocyte 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.