Brief DeNnitive Report

Insulin receptors are present on lymphoid cell lines (1) and activated murine and human lymphocytes (2, 3) with similar physicochemical properties to those on liver cells and adipocytes. Resting small lymphocytes apparently lack specific binding sites for insulin (2, 3), whereas they are present on mitogen-stimulated human (3) and rat (2) lymphocyte populations. Also, activated murine or human lymphocytes generated in mixed lymphocyte cultures express insulin receptors (4, 5). Our attention was drawn to the investigation of insulin receptors on T lymphocytes by an intriguing report citing the insulin receptor as a universal marker of activated lymphocytes (2). Because the above studies on lymphocyte insulin receptors have been done on heterogeneous lymphocyte populations, it was of interest to determine whether the insulin receptor is indeed expressed on all the various activated T and B cell subsets, or rather on some but not others. I f insulin receptors are expressed by a fraction of activated lymphocytes, can they be used as cell surface markers to define functional lymphocyte subpopulations or used as determinants of differentiation states of a given lymphocyte lineage? To investigate these questions, one can fractionate splenic lymphocytes into subsets based on cell surface markers (e.g., Thy-1, Lyt-1, Lyt-2, surface immunoglobulin) and examine these for insulin receptor expression. Another possibility would be to examine cloned lymphocyte cell lines. We decided to pursue the latter direction using murine T cell clones, which are H-2 restricted, influenza virus specific and antigen dependent for proliferation (6, 7). We recently reported (6) the isolation, characterization, and continuous propagation of these cloned T lymphocyte lines. The availability of these T cell clones affords the opportunity of examining insulin receptor expression on homogeneous, nontransformed cell lines with cytotoxic or helper function. Also, using a homogeneous T cell clone, we can determine whether the insulin receptor can be a marker of the activated vs. the resting state of a given T cell clone subsequent to antigenic stimulation. This report describes the expression of insulin receptors on noncytotoxic T lymphocyte clones subsequent to specific antigenic stimulation and the apparent lack of detectable insulin specific receptors on activated cytotoxic T cell clones.