The insulin receptor as a universal marker of activated lymphocytes

Although resting, rat thymus‐derived spleen lymphocytes do not bear insulin receptors, these receptors emerge upon the membrane of alloimmune rat T cells subsequent to skin grafting. These studies examine conditions that permit the emergence of lymphocyte insulin receptors upon T or B‐enriched rat lymphocyte populations. Allogeneic stimulation was accomplished in vivo by skin grafting from (Lewis × Brown Norway)F1 (LBN) to Lewis male rats or by Graft‐vs.‐host (GVH) reaction established by intraperitoneal injections of 2 × 108 Lewis leukocytes each week for a total of four injections into LBN animals. In vitro allogeneic stimulation was provided by one‐way mixed lymphocyte cultures between the same strains. Lastly, both T and B‐enriched populations were interacted with mitogens concanavalin A (Con A), phytohemagglutinin (PHA‐P), and lipopolysaccharide (LPS). The T‐enriched populations were highly enriched for T lymphocytes (90%) and macrophage‐depleted while B‐enriched populations contained nearly 85% B cells. Insulin receptors emerged upon T‐enriched cell populations consequent to allogeneic skin grafting with saturability, specificity and high affinity (kd = 1.1 nM) as well as after GVH. Responder strain lymphocytes developed an insulin receptor during allogeneic mixed lymphocyte cultures within 72 h of initiation. Specific insulin‐binding sites also appeared upon T‐enriched populations after culture with PHA‐P and Con A but not LPS. Conversely, B cells developed an insulin receptor after interactions with LPS but not PHA‐P or Con A. Anti‐Ig and complement but not rat anti‐T cell antibody abrogated the ability of LPS to induce an insulin receptor on B‐enriched cells. Binding specificity was demonstrated by the inhibition of [125I]‐labeled insulin in the order porcine insulin ≊ desalanine insulin > proinsulin ≫ desoctapeptide insulin with growth hormone exhibiting no such inhibition. These data demonstrate that a true insulin receptor appears upon both T and B cells consequent to activation. The lymphocyte insulin receptor is a universal marker of cellular activation as it is not restricted to clone or species and may be applied to B and T lymphocytes of mouse, rat and man.