Murine T cell-specific Ia antigens: monoclonal antibodies define an I-A-encoded T lymphocyte structure.

T lymphocytes express a unique I-A subregion-controlled surface molecule that is not expressed on B lymphocytes. We produced antisera and monoclonal antibodies recognizing this structure. Exhaustive B cell adsorption (A.TH X B10.HTT)F antiserum, produced against activated A.TL T cells, left antibodies that bind an I-Ak specificity on some B10.A(4R) T lymphocytes (11 +/- 2%, mean +/- SEM). Similarly, exhaustive B cell adsorption of (A/J X B10.MBR)F antiserum, produced against activated B10.A(5R) cells, left antibodies specific for an I-Ab determinant on B10.A(5R)T cells (17 +/- 2%). We fused A.TL-immune (A.TH X B10.HTT)F splenocytes with NS-1 myeloma cells and identified antibody-producing hybrid cells by a fluorescent enzyme-linked immunosorbent microassay described herein. Eight monoclonal antibodies were selected; these lyse 7--26% of peripheral T cells from I-Ak strains. Thymocytes and bone marrow cells do not express the I-Ak T cells determinant. Exhaustive B cell adsorption did not remove I-Ak T cell-specific monoclonal antibodies.