The Ly-10 antigen is a marker of mouse-activated T lymphocytes.

Ly-10.1 is a lymphocyte surface antigen controlled by a gene linked to the Ly-1.1 locus and expressed on activated T helper, T suppressor (Ts), and cytotoxic T lymphocytes (CTL). In this report, we describe the following: 1) Ly-10 is a heterodimeric glycoprotein consisting of a 80,000 heavy and a 34,000 light chain. 2) Although mature CTL are Ly-10+ by negative selection with anti-Ly-10.1 and complement (C), CTL precursors reactive to allogeneic cells are Ly-10-. 3) Similarly, IL-2-producing effector T cells induced by Mls-incompatible cells and semiallogeneic stimulation are eliminated by anti-Ly-10.1 and C after activation but are not eliminated as precursors before activation. 4) In mixed lymphocyte culture with semiallogeneic cells, the frequency of Ly-10.1+ cells was highest on the 2nd to 5th day after stimulation, decreased by the 12th day, and increased after restimulation with fresh antigen as demonstrated by immunofluorescence, C-mediated lysis, and IL-2 production. 5) When spleen cells were treated with anti-Ly-10 and C before concanavalin A (Con A) activation, the suppressive activity in the Con A T blasts was reduced, suggesting that in normal mice, some Ts preexist in a Ly-10+ activated state. These results indicate that Ly-10 is a marker of activation of T cells, not expressed on precursor T cells and whose expression is both transient and dependent on the presence of antigen. The similarities in biochemical and cellular characteristics suggest that Ly-10 is a mouse homologue of the human lymphocyte activation marker 4F2.