We have purified the human T-cell growth factor (interleukin-2) receptor and have cloned, sequenced and expressed cDNAs corresponding to this receptor. We identify one gene, but two interleukin-2 receptor mRNAs which differ in their polyadenylation signals. We have isolated an additional cDNA that may correspond to an alternatively spliced mRNA that lacks a 216 base segment and appears to encode an altered membrane protein which cannot bind interleukin-2.

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Cyclosporin A (CsA) is a potent immunosuppressive agent, now gaining wide application in human organ transplantation. The immunosuppressive activity of CsA is at least in part due to inhibition of lymphokine production by activated T lymphocytes. Specifically, inhibition of T-cell growth factor (TCGF; also designated interleukin 2) production appears to be an important pathway by which CsA impairs T-cell function. To define further both the specificity of CsA and the level at which it interferes with lymphokine gene expression, we have studied its effects on TCGF mRNA accumulation as well as TCGF gene transcription. These studies were performed with a cloned human leukemic T-cell line (Jurkat, subclone 32), which can be induced with phytohemagglutinin and phorbol 12-myristate 13-acetate to produce large amounts of TCGF. In these cells, high levels of TCGF mRNA were present in induced but not in uninduced Jurkat cells as judged by hybridization to a cloned human TCGF cDNA probe. CsA completely inhibited induced TCGF mRNA accumulation at concentrations of 0.3-1.0 microgram/ml, whereas low levels of appropriately sized TCGF mRNA were present at 0.01 microgram/ml. In nuclear transcription experiments, CsA inhibited the synthesis of TCGF transcripts in a dose-dependent manner with complete inhibition at a concentration of 1 microgram/ml. In contrast, CsA did not inhibit the expression of two other inducible genes, TCGF receptor and HT-3. Further, HLA gene expression was also less affected than TCGF in CsA-treated cells. These data suggest a relatively selective action of CsA on TCGF gene transcription.

We demonstrate that purified interleukin 2 (IL-2) can directly upregulate IL-2 receptor expression on phytohemagglutinin-activated T lymphocytes maintained in culture until IL-2 receptor expression had markedly declined. The IL-2-induced increase in IL-2 receptor number is maximal within 12 hr, requires new RNA and protein synthesis, and is mediated by an interaction of ligand with the high-affinity receptors for IL-2. IL-2 stimulation results in increased accumulation of IL-2 receptor mRNA within 4 hr, while an increase in IL-2 receptor gene transcription is detected within 30 min in isolated nuclei. In addition, IL-2 incubation results in increased amounts of c-myc and transferrin receptor mRNA, but it does not augment levels of mRNA encoding the fi chain of the T-cell receptor for antigen. These results demonstrate that IL-2 can directly upregulate transcription and expression of its own receptor and, therefore, indicate that IL-2 may regulate IL-2-dependent immune responses, in part, by influencing the expression of IL-2 receptors.

Several antigen-nonspecific, genetically unrestricted factors derived from T cells have been shown to play a role in the regulation of B cell responses (1-9). One such factor, designated B cell growth factor (BCGF-1 or BSF-1), ~ appears to be required for the proliferation of a subset of B cells after interaction with antigen or antiimmunoglobulin molecules. A second series of factors, called B cell differentiation (BCDF) or T cell-replacing factors (TRF), is involved in the terminal maturation of proliferating B cells into immunoglobulin-secreting cells. There has been controversy regarding the possible involvement of T cell growth factor or interleukin 2 (IL-2) in B cell responses and specifically the ability of this growth factor to act directly on B lymphocytes. The proponents of a direct action of IL-2 on B cells showed that depletion of IL-2 from cofactor-rich supernatants by absorption on IL-2-dependent T cell lines also removed a factor required for B cell differentiation (4, 5, 10). Furthermore, there was a strict correlation between the levels of IL-2 and one of the B cell-specific factors required for antibody production (4). This view that IL-2 acts directly on B cells has been challenged, since both mouse and human IL-2 have been distinguished from B cell growth and differentiation factors (7-11). The IL-2-containing supernatants generally used in the previous studies (the supernatant of the FS6-14.13 line) also contained BCGF and one or more TRFs (9). Furthermore, IL-2 was not absorbed from cofactor-rich supernatants by incubation with lipopolysaccharide (LPS)-stimulated splenic lymphoblasts (4). Finally, radiolabeled IL-2 did not bind to LPS-stimulated B cells or to either of the two Burkitt's lymphoma B cell lines examined (Raji and Daudi) suggesting that B cells do not manifest receptors for IL-2 (12).We have reexplored the possibility that certain activated B cells display receptors for IL-2 using the anti-Tac monoclonal antibody produced in our laboratory (13,14). This monoclonal antibody identifies the human membrane receptor for 16,17). The observations that led to this conclusion include: (a) antiAbbreviations used in this paper: BCDF, B cell differentiation factor; BCGF, B cell growth factor; EBV, Epstein-Barr virus; IL-2, interleukin 2; LPS, lipopolysaccharide; NWSM, Nocardia watersoluble mitogen; PWM, pokeweed mitogen; SDS, sodium dodecyl sulfate; SLO, Streptolysin-O; WGA, wheat germ agglutinin.