A lymphocyte differentiation and activation antigen, CZ-1, that distinguishes between CD8+ and unstimulated CD4+ T lymphocytes.

We report the generation and cellular reactivity of a novel rat IgM monoclonal antibody (mAb), CZ-1, made against mouse natural killer (NK) cells activated in vivo. mAb CZ-1 recognizes a molecule whose properties are consistent with that of a trypsin-sensitive, non-phosphatidyl inositol-linked sialoglycoprotein. The expression of the antigen recognized by mAb CZ-1 is restricted mostly to cells of the lymphoid lineage. The antigen is expressed on 10%-25% of bone marrow cells and 3%-5% of thymocytes. Analysis of thymocyte subpopulations indicates expression of the CZ-1 antigen on 100% of the NK1.1+, 27% of the CD4-CD8-, 1.1% of the CD4+CD8+, 1.1% of the CD4+CD8-, and 33% of the CD4-CD8+ cells. In the spleen, the CZ-1 antigen is expressed on B lymphocytes, NK cells, and virtually all CD8+ T lymphocytes. Most unstimulated CD4+ splenic T lymphocytes, monocytes and polymorphonuclear cells, with the notable exception of basophils, do not react with mAb CZ-1. CD4+ T cells activated in vivo by virus infection or in vitro by anti-CD3 and interleukin-2 express the CZ-1 antigen. These results indicate that mAb CZ-1 identifies a novel inducible lymphocyte activation/differentiation antigen that distinguishes between thymic and unstimulated splenic CD4+ and CD8+ T lymphocytes. This mAb will be a useful tool in the identification of lymphocyte subpopulations and in the study of the ontogeny and activation of these cells.