Eukaryotic cells respond to different extracellular stimuli by recruiting homologous signalling pathways that use members of the MEKK, MEK and ERK families of protein kinases. The MEKK-->MEK-->ERK core pathways of Saccharomyces cerevisiae may themselves be regulated by members of the STE20 family of protein kinases. Here we report specific activation of the mammalian stress-activated protein kinase (SAPK) pathway by germinal centre kinase (GCK), a human STE20 homologue. SAPKs, members of the ERK family, are activated in situ by inflammatory stimuli, including tumour-necrosis factor (TNF) and interleukin-1, and phosphorylate and probably stimulate the transactivation function of c-Jun. Although GCK is found in many tissues, its expression in lymphoid follicles is restricted to the cells of the germinal centre, where it may participate in B-cell differentiation. Activation of the SAPK pathway by GCK illustrates further the striking conservation of eukaryotic signalling mechanisms and defines the first physiological function of a mammalian Ste20.

We studied 17 patients with severe systemic necrotizing vasculitis over an 11-year-period. Sixteen patients were treated daily with cyclophosphamide (2 mg per kilogram per day), and one was treated with azathioprine (2 mg per kilogram per day). Before entering the study, all patients had active and progressive disease, even though 16 patients had been receiving corticosteroids that had caused severe and often incapacitating toxic side effects. Three patients died during the study. Complete and often dramatic remissions occurred in the surviving 14 patients, who were then placed on alternate-day corticosteroid treatment with continuation of cyclophosphamide. Corticosteroids were later discontinued in seven patients. The mean duration of remission was 22 months (range, two to 61). No patient showed recurrence of disease during treatment with cytotoxic agents.

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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.

Immunodeficiency disorders have provided much information on the development and interaction of the various B and T lymphoid components in the immune system of man. As the lymphoid system becomes increasingly divided into functional subsets of cells it will be important to find immunodeficiencies affecting newly discovered cell types. Natural killer (NK) cells are a recently described but ill-defined subpopulation of lymphocytes which is thought to play an important part in surveillance against tumour development. Mice homozygous for the beige gene were found to have a selective deficiency in NK function and were more susceptible to transplantation of syngeneic tumours as predicted. We report here that patients carrying the analogous, autosomal recessive Chediak-Higashi (CH) gene have a profound defect in their ability to spontaneously lyse various tumour cells in vitro by either antibody-dependent or independent mechanisms. Since other cell-mediated cytolytic functions were relatively normal, these results suggest that the beige or Chediak-Higashi gene in both man and mouse controls NK function.

In the preceding (1) paper we showed that human Ch6diak-Steinbrinck-Higashi syndrome (C-HS) 1 donors had a marked impairment in natural-killer (NK)-cell function. It was then relevant to ask whether this defect was selective for NK cells as previously observed in the mouse C-HS model (2) or whether other effector-cell types were also defective. Because the C-HS is thought to involve a single recessive gene (3), it was hoped that these experiments would help clarify the relationship between NK cells and a variety of other cell types capable of lysing tumor-cell targets, including K cells involved in antibody-dependent cell-mediated cytotoxicity (ADCC), T cells, monocytes, and neutrophils. In this paper, we show that lymphocyte-mediated ADCC against tumor-cell targets is also defective, whereas ADCC mediated by both mononuclear cells and polymorphonuclear leukocytes (PMN) against erythrocyte targets is normal. Cytolysis of tumor cells by other effectors (T cells, monocytes, and PMN) was also relatively normal. These results suggest that C-HS patients may have a quite selective impairment in immunologic function. The implication of these findings for immune surveillance is discussed.

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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.