A new thymocyte membrane differentiation antigen for mouse and rat.

A new thymocyte membrane-brain antigenic system is defined for the mouse and rat. Monoclonal antibody NIM-M129 recognizes a membrane antigen that has a similar size to Thy-1 (20-23 kd) but entirely different tissue distribution. It is absent from cortisone-resistant thymocytes, murine peripheral T cells, T-cell blasts, and T-cell lymphomas, or rat bone marrow. However, the determinant exhibits a quantitative difference in expression on thymocytes of Thy-1a (low) and Thy-1b (high) mice, with intermediate values for their F1 progeny. Backcross and F2 segregation tests between CBA and CBA-Thy-1a congenic lines established firm genetic linkage between Thy-1 and the level of epitope expression on the thymocyte cell surface.