Involvement of 4F2 antigen expressed on the MHC-negative target cells in the recognition of murine CD3+ CD4− CD8− αβ (Vα4/Vβ2) T cells

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Abstract
T cells of an unique phenotype (CD3+CD4−CD8− αβ TCR+) develop in vitro from the hematopoietlc progenitors, the majority of which carry homologous αβ TCR (Vα4Jα28/Vβ2Dβ1.1Jb.β2.6). In the present study, antigen corresponding to the particular αβ TCR was investigated, taking advantage of the fact that growth of T cell hybridomas was arrested by their TCR stimulation. Results indicated that both syngenelc and allogeneic thymocytes, particularly from newborn mice, could specifically inhibit the proliferation of a T cell hybridoma with the Vα4/Vβ2 TCR (15H1.2). Proliferation of neither TCR-missing hybridoma subciones nor those with unrelated αβ TCRs was affected at all. It was also found that embryonal carcinoma (EC) cells without classical MHC antigens could specifically inhibit the proliferation of 15H1.2 cells. We then raised a mAb, 14.37, against an EC line, OTF9, that could interfere with the ability of them to inhibit the growth of 15H1.2. Pretreatment of 15H1.2 cells with anti-V&b.β2 and OTF9 cells with 14.37 mAb respectively completely abrogated the growth inhibition of 15H1.2 by OTF9. The 14.37 antigen was a 120 kDa heterodimer glycoprotein consisting of 85 and 36 kDa proteins. In normal lymphold tissues, the expression of 14.37 antigen exhibited an apparently inverse relationship with that of class I MHC antigens. Thus, ontogenlcally it was strongly expressed in fetal and newborn mice, rather rapidly declined thereafter, and remained at very low levels in adult organs. In a given stage, the distribution of 14.37 antigen and class I MHC was rather exclusive to each other. Molecular cloning of the 14.37 antigen revealed it to be a murine homolog of human 4F2 heavy chain. Collectively, the present results suggested that a subset of CD3+ CD4− CD8− αβ T cells could specifically recognize the fetal/activation antigen, 4F2, on the target cells in a MHC-independent fashion.

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