The p75 peptide is the receptor for interleukin 2 expressed on large granular lymphocytes and is responsible for the interleukin 2 activation of these cells.
There are at least two interleukin 2 (IL-2) binding peptides: one is the Mr 55,000 peptide (p55) reactive with the anti-Tac monoclonal antibody, and the other is a Mr 75,000 non-Tac IL-2 binding peptide (p75). Independently existing Tac or p75 peptides represent low-affinity IL-2 receptors, whereas high-affinity IL-2 receptors are expressed when both peptides are present and associated in a receptor complex. It has long been known that normal large granular lymphocytes (LGL) or leukemic cells from the patients with abnormal expansions of LGL can be activated by IL-2 not only to more-potent natural killer cells but also to effectors of lymphokine-activated killer (LAK) activity, although they do not express the Tac peptide. In the present study, using cross-linking methodology, we found that normal LGL and leukemic LGL from all individuals tested expressed the p75 IL-2 binding peptide but did not express the Tac peptide. These LGL leukemia cells made proliferative responses to IL-2 but required a much higher concentration than that required for the proliferation of normal phytohemagglutinin-stimulated T lymphoblasts that express high-affinity receptors. Furthermore, the addition of IL-2 to Tac-negative LGL leukemic cells augmented transcription of the Tac gene and induced the Tac peptide. Neither the IL-2-induced proliferation nor the up-regulation of Tac gene expression was inhibited by the addition of anti-Tac. These results strongly suggest that the p75 peptide is responsible for IL-2-induced activation of LGL and that the p75 peptide alone can mediate an IL-2 signal. Thus, the p75 peptide may play an important role in the IL-2-mediated immune response not only by participating with the Tac peptide in the formation of the high-affinity receptor complex on T cells but also by contributing to the initial triggering of LGL activation so that these cells become efficient natural killer and lymphokine-activated killer cells.
D002455:Cell Division / Q000187:drug effects; D002469:Cell Separation; D005786:Gene Expression Regulation; D006801:Humans; D007376:Interleukin-2 / Q000378:metabolism*; D007938:Leukemia / Q000097:blood*; D008214:Lymphocytes / Q000378:metabolism*; D008970:Molecular Weight; D011971:Receptors, Immunologic / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D015375:Receptors, Interleukin-2; D014158:Transcription, Genetic
D007376:Interleukin-2; D011971:Receptors, Immunologic; D015375:Receptors, Interleukin-2