Interleukin-1 (IL-1), a peptide hormone produced by activated macrophages, possesses the ability to modulate the proliferation, maturation and functional activation of a broad spectrum of cell types and may play a major role in the initiation and amplification of immune and inflammatory responses through its action on these diverse cell populations. IL-1 exhibits microheterogeneity in terms of its relative molecular mass (Mr, 13,000-19,000) and charge properties, and although murine IL-1 has been purified and some of its basic structure-function relationships have been elucidated, it has proved difficult to prepare sufficient amounts of IL-1 for direct and detailed sequence and structural studies. Here we report the cloning, sequence analysis and expression of murine IL-1 cDNA in Escherichia coli. The IL-1 cDNA codes for a polypeptide precursor of 270 amino acids. Biologically active IL-1 was produced in E. coli by expressing the carboxy-terminal 156 amino acids of the IL-1 precursor.

To investigate the mechanism by which immune activation augments replication of the human immunodeficiency virus type 1 (HIV-1) in infected T cells, four different classes of T cell mitogens were evaluated for their effects on the HIV-1 long terminal repeat (LTR). Phytohemagglutinin (PHA), a mitogenic lectin; phorbol 12-myristic 13-acetate, a tumor promoter; ionomycin, a calcium ionophore; and tat-1, the trans-activator protein from the human T cell leukemia/lymphoma virus type I (HTLV-I) each stimulated the HIV-1 LTR. Studies of deleted forms of the LTR supported a central role in these responses for the HIV-1 enhancer, which alone was sufficient for mitogen inducibility, but also suggested that other 5' positive and negative regulatory elements contribute to the overall magnitude of the response. Synergistic activation of the HIV-1 LTR (up to several thousandfold) was observed with combinations of these mitogens and the HIV-1--derived tat-III protein. Cyclosporin A, an immunosuppressive agent, inhibited PHA-mediated activation of the HIV-1 LTR but was without effect in the presence of other mitogens. Thus, HIV-1 gene expression and replication appear to be regulated, via the HIV-1 LTR, by the same mitogenic signals that induce T cell activation.

Two evolutionarily distinct families of human retroviruses, the human immunodeficiency viruses (HIV) and the human T-cell leukaemia viruses (HTLV), have been defined (reviewed in ref. 1). Although these virus groups share tropism for human CD4+ T cells, they differ markedly in primary sequence, genetic organization and disease association (AIDS versus adult T-cell leukaemia), but show similar general strategies for the regulation of viral gene expression. Each encodes a protein able to trans-activate transcription from the homologous viral long terminal repeat (tat in HIV, tax in HTLV), although these proteins act by different mechanisms and do not appear to be interchangeable. Each virus also produces a second trans-acting protein that induces the expression of the unspliced messenger RNAs encoding the viral structural proteins (rev in HIV and rex in HTLV). Here we show that the rex protein of HTLV-I can functionally replace the rev protein of HIV-1 in transient expression assays. This genetic complementation by rex is adequate for the rescue of a replication-defective rev mutant of HIV-1. This unexpected shared function between the structurally distinct rex and rev proteins emphasizes the importance of this highly conserved pathway for the regulation of human retrovirus gene expression.

Although activated human T and B lymphocytes express both high-affinity and low-affinity membrane receptors for interleukin-2 (IL-2), the structural features that distinguish these receptors have remained unresolved. The high-affinity receptors appear to mediate IL-2 induced T cell growth and internalization of IL-2, whereas no function has yet been ascribed to the low-affinity receptors. The Tac antigen is an IL-2 binding protein of relative molecular mass 55,000 (Mr 55K) that participates in the formation of both high- and low-affinity receptors. But Tac complementary DNA transfection and membrane fusion studies have suggested that additional T-cell components are required to produce high-affinity IL-2 receptors. In this study, we report the identification of a second human IL-2 binding protein that (1) has an Mr of approximately 70K, (2) lacks reactivity with the anti-Tac antibody, (3) binds IL-2 with intermediate affinity and (4) is present on the surface of resting T cells, large granular lymphocytes (natural killer cells), and certain T and B cell lines in the absence of the Tac antigen. Chemical crosslinking of 125I-labelled IL-2 bound to high-affinity IL-2 receptors produces labelling of both the p70 protein and the Tac antigen and the anti-Tac antibody blocks the crosslink detection of both of these proteins. Expression of Tac cDNA in a T cell line expressing the p70 protein, but lacking both Tac and high-affinity receptors, results in the reconstitution of high-affinity IL-2 receptors in these cells. Together, these findings suggest that the high-affinity human IL-2 receptor may be a membrane complex composed of at least the p70 protein and Tac antigen.

Anti-Tac effectively blocked the IL-2-induced proliferative response in these cells, but failed to alter the enhancement of cytotoxicity. Analysis of NK cytoplasmic RNA isolated at various time points after IL-2 stimulation revealed the rapid induction of c-myb and Tac gene expression that was also not inhibited by the anti-Tac antibody. These findings suggest that IL-2 binding to the p70 receptor constitutively expressed on the surface of NK cells may mediate both the development of increased cytolytic activity and rapid changes in gene expression. The activation of the Tac gene may in turn permit the formation of the high affinity IL-2 receptor complex (comprised of at least the Tac and p70 proteins) that appears to transduce the requisite signals involved in NK cell proliferation.

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