Role of interleukin 6 for differential responsiveness of naive and memory CD4+ T cells in CD2-mediated activation

Interleukin-6: An Under-Appreciated Inducer of Thermogenic Adipocyte Differentiation

Adipose tissue inflammation is a key factor leading to obesity-associated immune disorders, such as insulin resistance, beta cell loss in the pancreatic islets, meta-inflammation, and autoimmunity. Inhibiting adipose tissue inflammation is considered a straightforward approach to abrogate these diseases. However, recent findings show that certain pro-inflammatory cytokines are essential for the proper differentiation and functioning of adipocytes. Lipolysis is stimulated, and the thermogenic competence of adipocytes is unlocked by interleukin-6 (IL-6), a cytokine that was initially recognized as a key trigger of adipose tissue inflammation. Coherently, signal transducer and activator of transcription 3 (STAT3), which is a signal transducer for IL-6, is necessary for thermogenic adipocyte development. Given the impact of thermogenic adipocytes in increasing energy expenditure and reducing body adiposity, functions of IL-6 in the adipose tissue have gained attention recently. In this review, we show that IL-6 signaling may protect from excess fat accumulation by stimulating thermogenesis in adipocytes.

Impact of interleukin-6 on T cells in kidney transplant recipients

Interleukin-6 (IL-6), a multifunctional proinflammatory cytokine, plays a key role in T cell activation, survival, and differentiation. Acting as a switch that induces the differentiation of naïve T cells into Th17 cells and inhibits their development into regulatory T cells, IL-6 promotes rejection and abrogates tolerance. Therapies that target IL-6 signaling include antibodies to IL-6 and the IL-6 receptor and inhibitors of janus kinases; several of these therapeutics have demonstrated robust clinical efficacy in autoimmune and inflammatory diseases. Clinical trials of IL-6 inhibition in kidney transplantation have focused primarily on its effects on B cells, plasma cells, and HLA antibodies. In this review, we summarize the impact of IL-6 on T cells in experimental models of transplant and describe the effects of IL-6 inhibition on the T cell compartment in kidney transplant recipients.

Systems Immunology Analyses of STAT1 Gain-of-Function Immune Phenotypes Reveal Heterogeneous Response to IL-6 and Broad Immunometabolic Roles for STAT1

Patients with STAT1 gain-of-function (GOF) pathogenic variants have enhanced or prolonged STAT1 phosphorylation following cytokine stimulation and exhibit increased yet heterogeneous susceptibility to infections, autoimmunity, and cancer. Although disease phenotypes are diverse and other genetic factors contribute, how STAT1 GOF affects cytokine sensitivity and cell biology remains poorly defined. In this study, we analyzed the immune and immunometabolic profiles of two patients with known pathogenic heterozygous STAT1 GOF mutation variants. A systems immunology approach of peripheral blood cells from these patients revealed major changes in multiple immune cell compartments relative to healthy adult and pediatric donors. Although many phenotypes of STAT1 GOF donors were shared, including increased Th1 cells but decreased class-switched B cells and plasmacytoid dendritic cell populations, others were heterogeneous. Mechanistically, hypersensitivity for cytokine-induced STAT1 phosphorylation in memory T cell populations was particularly evident in response to IL-6 in one STAT1 GOF patient. Immune cell metabolism directly influences cell function, and the STAT1 GOF patients shared an immunometabolic phenotype of heightened glucose transporter 1 (GLUT1) and carnitine palmitoyl transferase 1A (CPT1a) expression across multiple immune cell lineages. Interestingly, the metabolic phenotypes of the pediatric STAT1 GOF donors more closely resembled or exceeded those of healthy adult than healthy age-similar pediatric donors, which had low expression of these metabolic markers. These results define new features of STAT1 GOF patients, including a differential hypersensitivity for IL-6 and a shared increase in markers of metabolism in many immune cell types that suggests a role for STAT1 in metabolic regulation of immunity.

Role of IL-6 in the commitment of T cell subsets

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IL-6 is a non-redundant differentiation factor for Th17 cells and Tfh cells.

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The induction of ROR-γt⁺ Treg cells in the lamina propria depends on IL-6.

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Generation of distinct T helper cell subsets might depend on different IL-6 signaling modalities.

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IL-6-directed therapies must consider the disease-relevant IL-6 signaling modality.

IL-6 gained much attention with the discovery that this cytokine is a non-redundant differentiation factor for Th17 cells and T follicular helper cells. Adaptive immune responses to fungi and extracellular bacteria are impaired in the absence of IL-6. IL-6 is also required for the induction of ROR-γt⁺ Treg cells, which are gatekeepers of homeostasis in the gut lamina propria in the presence of commensal bacteria. Conversely, severe immunopathology in T cell-mediated autoimmunity is mediated by Th17 cells that rely on IL-6 for their generation and maintenance. Recently, it has been discovered that the differentiation of these distinct T helper cell subsets may be linked to distinct signaling modalities of IL-6. Here, we summarize the current knowledge on the mode of action of IL-6 in the differentiation and maintenance of T cell subsets and propose that a context-dependent understanding of the impact of IL-6 on T cell subsets might inform rational IL-6-directed interventions in autoimmunity and chronic inflammation.

Activation of naïve CD4+ T cells re-tunes STAT1 signaling to deliver unique cytokine responses in memory CD4+ T cells

The cytokine IL-6 controls the survival, proliferation and effector characteristics of lymphocytes through activation of the transcription factors STAT1 and STAT3. While STAT3 activity is an ever-present feature of IL-6 signaling in CD4⁺ T cells, prior T-cell receptor activation limits the IL-6 control of STAT1 in effector and memory populations. Here we show that STAT1 phosphorylation in response to IL-6 was regulated by protein tyrosine phosphatases (PTPN2, PTPN22) expressed in response to the activation of naïve CD4⁺ T cells. Transcriptomic and chromatin immunoprecipitation-sequencing of IL-6 responses in naïve and effector memory CD4⁺ T cells showed how the suppression of STAT1 activation shaped the functional identity and effector characteristics of memory CD4⁺ T cells. Thus, protein tyrosine phosphatases induced by activation of naïve T cells determined the way activated or memory CD4⁺ T cells sensed and interpreted cytokine signals.

The modulation of PPARγ1 and PPARγ2 mRNA expression by ciglitazone in CD3/CD28-activated naïve and memory CD4+ T cells

Given their roles in immune regulation, the expression of the nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ) 1 and 2 isoforms was investigated in human naïve (CD45RA+) and memory (CD45RO+) CD4+ T cells. Stimulation of both types of cells via the CD3/CD28 pathway resulted in high expression of both PPARγ receptors as measured by real-time PCR. Treatment with the PPARγ agonist, ciglitazone, increased PPARγ1 expression but decreased PPARγ2 expression in stimulated naïve and memory cells. Furthermore, when present, the magnitude of both PPARγ receptors expression was lower in naïve cells, perhaps suggesting a lower regulatory control of these cells. Similar profiles of selected proinflammatory cytokines were expressed by the two cell types following stimulation. The induction of PPARγ1 and suppression of PPARγ2 expressions in naïve and memory CD4+ T cells in the presence of ciglitazone suggest that the PPARγ subtypes may have different roles in the regulation of T-cell function.

Selective expansion of CD16highCCR2- subpopulation of circulating monocytes with preferential production of haem oxygenase (HO)-1 in response to acute inflammation

Monocytes are composed of two distinct subpopulations in the peripheral blood as determined by their surface antigen expressions, profiles of cytokine production and functional roles played in vivo. We attempted to delineate the unique functional roles played by a minor CD16(high)CCR2(-) subpopulation of circulating monocytes. They produced significant levels of interleukin (IL)-6 and tumour necrosis factor (TNF)-alpha, but very low levels of IL-10 upon in vitro stimulation. Characteristic profiles of cytokine production were confirmed by stimulating purified subpopulations of monocytes after cell sorting. It was noteworthy that freshly isolated CD16(high)CCR2(-) monocyte subpopulations produced significant levels of haem oxygenase (HO)-1, whereas the major CD16(low)CCR2(+) subpopulation produced little. These results were contrary to the generally accepted notion that the CD16(high)CCR2(-) monocyte subpopulation plays a predominantly proinflammatory role in vivo. The CD16(high)CCR2(-) subpopulation increased in Kawasaki disease and influenza virus infection. In accord with this, HO-1 mRNA expression by mononuclear cells was significantly increased in these illnesses. These results indicate that CD16(high)CCR2(-) subpopulations are of a distinct lineage from CD16(low)CCR2(+) monocytes. More importantly, they may represent a monocyte subpopulation with a unique functional role to regulate inflammation by producing HO-1 in steady state in vivo.

The CTA1-DD vaccine adjuvant binds to human B cells and potentiates their T cell stimulating ability

The present study demonstrates that the novel CTA1-DD-adjuvant, which combines the full enzymatic activity of the A1 subunit of cholera toxin (CT) with an immunoglobulin-binding domain of Staphylococcus aureus protein A (SpA), binds directly to human peripheral blood B lymphocytes of all classes and greatly augments B cell functions in vitro. These effects were reflected in strongly enhanced co-stimulation, resulting in augmented T cell responses to polyclonal-specific as well as Ag-specific activation in vitro. The CTA1-DD-adjuvant had pronounced effects on B cell functions with up-regulated expression of several important activation and co-stimulatory molecules, in particular CD86. Moreover, the adjuvant alone promoted cytokine and chemokine secretion by targeted B cells and in the presence of additional stimuli proliferative responses were augmented. These effects were dependent on the whole enzymatically active CTA1-DD molecule, since DD alone had no effects on the B cells. Collectively our data suggest that CTA1-DD acted via enhanced co-stimulation, which holds promise as to the use of CTA1-DD as a non-toxic adjuvant in future vaccines for human use.

Heme oxygenase-1 production by peripheral blood monocytes during acute inflammatory illnesses of children

Monocytes play key roles both in innate and adaptive antigen-specific immunity and they constitute critical components of the immune responses. Although most of the monocyte-derived cytokines exhibit proinflammatory functions in vivo, heme oxygenase-1 (HO-1), an inducible heme-degrading enzyme, exerts potent anti-inflammatory effect through production of carbon monoxide and bilirubin. We compared HO-1 production by monocytes in vivo in various acute inflammatory illnesses and in normal controls. Freshly isolated monocytes produced little HO-1 as detected by immunohistochemistry, but it was rapidly induced in vitro upon stimulation. HO-1 production by monocytes was selective because it was not induced in other leukocyte populations, including granulocytes and lymphocytes. Monocytes from acute inflammatory illnesses, such as Kawasaki disease and acute infectious diseases, viral or bacterial, produced significant levels of HO-1, as detected by flow cytometry, immunohistochemistry, and reverse transcription polymerase chain reaction. Quantitative analysis of HO-1 mRNA expression by real-time polymerase chain reaction revealed that monocytes from controls exhibited low, but significant levels of HO-1 mRNA, indicating that circulating monocytes produce HO-1 constantly, in response to basal level of oxidative stress encountered daily. Significantly elevated HO-1 mRNA levels seen in acute inflammatory illnesses suggest that monocyte HO-1 production serve as potent anti-inflammatory agent to control excessive cell or tissue injury in the presence of oxidative stress and cytokinemia.

Interleukin-6 and interleukin-12 participate in induction of a type 1 protective T-cell response during vaccination with a tuberculosis subunit vaccine

We examined the role of cytokines in the development of gamma interferon (IFN-gamma)-secreting protective T cells following immunization with a culture filtrate subunit vaccine against Mycobacterium tuberculosis containing the adjuvant dimethyldioctadecylammonium bromide (DDA). Depletion of either interleukin-6 (IL-6) or IL-12 with specific neutralizing antibodies during vaccination reduced the priming of T cells for antigen-specific proliferation and IFN-gamma secretion. Such reduction was also observed in IL-6 gene-disrupted mice as compared to wild-type animals. IL-6 was found to play a role in the initial differentiation of Th1 cells but not in their expansion. The defect found after IL-6 depletion or in IL-6-knockout mice was compensated by the inclusion of recombinant mouse IL-12 in the vaccine. The induction of protective immunity against an intravenous or an aerosol challenge with live, virulent M. tuberculosis was markedly reduced by neutralizing either IL-6 or IL-12 during immunization with the vaccine. Likewise, the effects of IL-6 neutralization were partially reversed by including IL-12 in the vaccine. Our data point to an important role of IL-6 and IL-12 in the generation of cell-mediated immunity to tuberculosis.

Developmental changes and functional properties of human memory T cell subpopulations defined by CD60 expression

The present study was undertaken to examine developmental changes of T cells expressing CD60 and their functional properties. Three-color immunofluorescence analysis revealed that the CD60 antigen was preferentially expressed on a proportion of memory (CD45RO+) CD4+ T cells, but less on memory CD8+ T cells, while this antigen is undetectable in naive (CD45RO-) T cells. A frequency of memory CD4+ T cells expressing CD60 in the peripheral blood was negligible in newborns and gradually increased with advancing age. CD60+ memory CD4+ T cells showed stronger proliferative responses to PPD and produced higher levels of IL-4 and IL-10 than CD60- ones, whereas production of IL-2 and IFN-gamma was similarly found in both cell subpopulations. In addition, it was shown that efficient helper activity for Ig production by B cells was predominated in CD60+ memory CD4+ T cells. These results suggest that CD60 may be primarily expressed on the functionally differentiated memory effector cells among circulating CD45RO+ CD4+ T cells.

15-Deoxyspergualin inhibits interleukin 6 production in in vitro stimulated human lymphocytes

Experimental data show that relatively low concentrations of 15-deoxyspergualin (DSG) inhibit the induction of cytotoxic T lymphocytes (CTL) and the generation of antibody-producing cells. Considerably higher concentrations of DSG are required to inhibit proliferative responses. In this in vitro study, the effects of DSG on CTL induction, on proliferative responses induced by different stimuli, and on the production of interleukins IL-1, IL-2 and IL-6 and IFN-gamma (gamma-interferon) were assessed and compared with the effects of CsA (cyclosporine A) and/or FK506. We confirmed the suppressive action of DSG on the generation of CTL. Quite unexpectedly, however, we found that, although DSG did not affect the proliferative response to allogeneic lymphocytes or a superantigen, it did inhibit proliferation of peripheral blood leucocytes (PBL) stimulated with Staphyloccus aureus. DSG was active even when added on day 2 of in vitro culture, suggesting that DSG does not inhibit early events. The fraction of CD3+ lymphoblasts and the CD4/CD8 ratio was lower in cells stimulated by S. aureus in the presence of DSG, showing a selective effect on CD3+CD4+ responder T lymphocytes. The proportion of IL-2 receptor (CD25) positive cells was also reduced by DSG treatment. Moreover, we found that DSG inhibited the proliferation induced by PHA (phytohaemagglutinin) but not by Con A (concanavalin A). This effect of DSG was time-dependent, since PHA induced proliferation was not affected until day 4 after stimulation, and indicated that DSG may inhibit proliferation induced via a CD2- but not via a CD3-mediated pathway. DSG did not influence the production of IL-2 or IFN-gamma or the lipopolysaccharide induced production of IL-2 or IL-6. In contrast, the production of IL-6 was inhibited when cells were stimulated by allogeneic lymphocytes, S. aureus, PHA or Con A. This suggested to us that the DSG-suppressed IL-6 production could be the basis for the other observed effects. We tried to mimic the DSG effects with antibodies and indeed found that the IL-6 specific antibodies had similar effects. Furthermore, recombinant IL-6 completely overcame the suppressive effects of DSG on S. aureus and PHA induced proliferation, whereas addition of IL-6 to DSG treated PBL only partly restored the cytotoxic activity of lymphoblasts induced by allogeneic cells. Thus, the inhibitory effect of DSG on de novo synthesis of IL-6 could explain some of its immunosuppressive effects, but additional DSG-sensitive steps are obviously involved in CTL induction and differentiation.

Cytokine expression by high-density human lymphocytes

T lymphocytes spend much of the time as small non-cycling cells. To determine the pattern of cytokine expression in such resting cells, they were purified from human peripheral blood mononuclear cells (PBMC) on the basis of high buoyant density. The cells were stimulated and cytokine mRNA expression was assessed by reverse transcription-polymerase chain reaction (RT-PCR). Expression of interleukin-2 (IL-2), IL-3 and interferon-gamma (IFN-gamma) was similar in high-density lymphocytes and in unfractionated PBMC. In contrast, the high-density lymphocytes expressed less IL-4 than PBMC, and little or no IL-5. Because a substantial minority of the high-density lymphocytes was CD45RO+, the presence of this marker was not an indicator of the ability to express IL-4 and IL-5. In the high-density lymphocytes, IFN-gamma expression was confined to the CD45RO+ fraction, whereas IL-2 was expressed by both CD45RO+ and CD45RO- subsets. To assess whether high-density lymphocytes could give rise to cells with a broader range of inducible cytokine expression, they were activated and then restimulated between 10 and 22 days of culture. Cells derived from both the CD45RO+ and CD45RO- fractions of high-density lymphocytes expressed IL-5 after restimulation. Thus the high-density lymphocyte population has the potential to acquire a broader range of inducible cytokine expression.

The profiles of interleukin (IL)-2, IL-6, and interferon-gamma production by peripheral blood mononuclear cells from house-dust-mite-allergic patients: a role for IL-6 in allergic disease

We have developed a model to measure cytokine production by peripheral blood mononuclear cells (PBMC) in vitro. In this report, we examine the production of interleukin-2 (IL-2), IL-6, and interferon-gamma (IFN-gamma) by PBMC of house-dust-mite (Dermatophagoides pteronyssinus)-allergic subjects. When stimulated with specific allergen (D. pteronyssinus), PBMC of patients produced significant levels of IL-2 and high levels of IL-6, but little or no IFN-gamma. Nonatopic control PBMC also produced IL-6, although at lower levels, but no IL-2 or IFN-gamma. A ubiquitous antigen, streptokinase/streptodornase (SKSD), induced high levels of IL-2 in patients, but only low levels of IFN-gamma and IL-6. Nonatopic controls produced similar levels of IL-2 and IL-6, but high levels of IFN-gamma to SKSD. IL-2 and IFN-gamma levels induced by the T-cell mitogen phytohaemagglutinin (PHA) were similar in patient and control groups, but IL-6 levels were significantly lower in the patients. IgE synthesis in vitro was shown only in atopic PBMC cultures stimulated with specific allergen. The major points can be summarized as 1) IL-2 production by atopic patients in response to allergen; 2) IL-6 production to allergen by both atopic and nonatopic patients, but significantly increased in atopic patients; and 3) defective IFN-gamma production by atopic patients to both allergen and antigen.(ABSTRACT TRUNCATED AT 250 WORDS)

CD57+ T lymphocytes are derived from CD57- precursors by differentiation occurring in late immune responses

CD3+ T cells expressing the 110-kDa CD57 antigen are found in survivors of renal, cardiac and bone marrow transplants, in patients with acquired immune deficiency syndrome and in patients with rheumatoid arthritis. They are also present in normal individuals and expand upon ageing. They do not grow in culture and their role in the immune response is poorly understood. The expression of the various isoforms of the leukocyte common antigen (CD45) identifies a spectrum of differentiation in CD4+ and CD8+ T cells ranging from naive (CD45RA+CD45RBbrightCD45RO-) through early primed cells (CD45RA-RBbrightROdull) to highly differentiated memory cells which are CD45RA-RBdullRObright. CD45 isoforms expressed by CD57+ T cells showed distinct differences between CD4+ and CD8+ populations, but in each case indicated an advanced state of differentiation. The expression of T cell receptor V beta families was highly variable between individuals, but both CD57+ and CD57- cells show a full range of the specificities tested. V beta expression was more closely related within either the CD4+ or the CD8+ subsets, irrespective of CD57 expression, than between these subsets, suggesting a relationship between CD57+ and CD57- cells within the same T cell pool. This possibility was supported by experiments showing that CD3+CD57+ lymphocytes were similar to CD3+CD57- T cells in terms of the production of basic T cell cytokines [interleukin (IL)-2, IL-4, and interferon-gamma]. Furthermore, in vitro stimulation of CD3+CD57- T cells in secondary mixed leukocyte reaction or by co-culture with IL-2 and IL-4 induced the appearance of CD3+CD57+ cells with phenotypic and functional similarities to in vivo CD3+CD57+ cells. These data strongly suggest that the expression of CD57 is a differentiation event which occurs on CD57- T cells late in the immune response.

Role of interleukin-6 in the induction of protective T cells during mycobacterial infections in mice

Interleukin-6 (IL-6) has been shown to regulate numerous functions of the immune system including the differentiation of T-cell subpopulations. Here we examined the involvement of this cytokine in the in vivo generation of a population of T cells able to protect mice against mycobacterial infections. BALB/c mice were infected intravenously with Mycobacterium avium 2447 and anti-IL-6 monoclonal antibodies were administered intraperitoneally throughout the course of the infection. Control mice were able to control the mycobacterial proliferation 1 month after inoculation, whereas mice whose IL-6 had been blocked showed progressive bacterial growth. To distinguish a role for IL-6 associated to the induction or expression of immunity mediated by T cells, we immunized mice with M. bovis bacillus Calmette-Guérin (BCG) Pasteur and challenged them 2 months later with M. avium. One group of mice received anti-IL-6 during the BCG vaccination and another during the M. avium challenge. When M. avium proliferation was assessed at day 30 of the challenge, it was found that the administration of anti-IL-6 during vaccination reduced the protection afforded by BCG compared to administration of the isotype control antibody. No difference in bacterial proliferation was observed at day 30 of challenge when antibodies were administered during M. avium challenge. Our results show that protective T cells arise during M. avium infections in mice after differentiating in the presence of IL-6.

Activation of naive, memory and effector T cells

An increased understanding of the types of T-cell subsets that exist in vivo, their relationships to one another, and how to identify and isolate them or effect their generation, has led to a comprehensive view of the antigen-presenting cells (APCs) which may be active and regulatory during the course of an immune response. Recent studies show that naive T cells only respond efficiently to dendritic cells and activated B cells whereas memory and effector cells respond to all APC types to some extent, including resting B cells. High level co-stimulatory molecule expression largely explains why APCs such as dendritic cells are far more effective stimulators than resting B cells. The available data, therefore, suggest that the requirement for co-stimulation, and hence capacity to respond to various APCs, is largely a function of the differentiation state of the T cell, and that previous encounter with antigen fundamentally increases the ability of T cells to subsequently respond to antigen rechallenge.

The progressive differentiation of primed T cells is associated with an increasing susceptibility to apoptosis

Recent studies have suggested that T cell memory for recall antigens resides in clones of primed T cells with a short inter-mitotic half-life. In humans such cells express an isoform of the leukocyte common antigen termed CD45RO. Nevertheless, little is known of the fate of these primed T cells after initial activation, since no markers are available to distinguish recently primed cells from long-established clones. This report is focused on a spectrum of primed CD4+ T cells characterized by an inverse relationship between the expression of two CD45 epitopes: CD45RB and CD45RO. We show that primed CD4+ T cells progress through many cycles of division from a CD45RBbrightOdull to a CD45RBdullObright state, resulting in a highly skewed distribution of the T cell receptor variable region usage within this particular population. The progressive differentiation defined by the shift from CD45RBbright to CD45RBdull is paralleled by the gradual loss of bcl-2 and gain of Fas expression, two features associated with an increased propensity for apoptosis. At the same time, the highly differentiated CD45RBdull cells selectively lose the capacity to synthesize interleukin (IL)-2, a cytokine which is particularly effective in preventing T cell apoptosis, although they produce high levels of IL-4. The inability to produce adequate levels of IL-2 leads to the apoptosis of primed CD45RBdull cells, when they are stimulated in the absence of exogenous IL-2. These observations show the crucial dependence of highly differentiated T cells on the availability of exogenous IL-2, and suggest both a major constraint for the persistence of T cell memory maintained by continually cycling primed cells, and an important mechanism contributing to the maintenance of T cell homeostasis in vivo.

Differential expression and regulation of cytokine mRNAs in normal human CD45R T cell subsets

Cytokine mRNA expression was analyzed by reverse transcriptase (RT)/PCR in extensively purified normal peripheral CD4+CD45R T cell subsets. Both CD45RA+ and CD45 RO+ populations produced mRNAs for interleukin (IL)-2, IL-2 receptor (alpha chain), IL-6 receptor and tumour necrosis factor (TNF)-beta within 3-4 h of activation. Whilst IL-3 and RANTES were also expressed in both subsets, CD45RO+ cells were clearly the major producers of these cytokines. In contrast, mRNA transcripts for IL-1 alpha, IL-4, IL-5, IL-6, IL-10, interferon gamma (IFN-gamma) and the T cell receptor for IL-1 were almost exclusively induced in CD45RO+ T cells. A population of CD4+ T cells co-expressing intermediate levels of both CD45RA and CD45RO, namely CD45RA+/CD45RO+, appeared to be the major producers of IL-6. Addition of cycloheximide (CHx) 4 h after T cell activation resulted in substantial superinduction of IL-2 mRNA in the CD4+CD45RO+ population but had little effect on CD4+CD45RA+ cells. Taken together, these results show that normal CD4+CD45R T cell subsets exhibit distinct cytokine mRNA profiles and that these differ from the patterns displayed by Th1 and Th2 type T helper clones. Furthermore, they suggest for the first time that IL-2 mRNA turnover is differentially regulated in CD45R T cell subsets.

Increased interleukin 6 production by bronchoalveolar lavage cells in patients with active sarcoidosis

Alveolitis of sarcoidosis is characterized by activated alveolar macrophages (AMs) and T cells. The mediators interleukin-1 (IL-1) and interleukin 6 (IL-6) released by AMs represent essential factors for the progression of the T cells in the cell cycle. The role of IL-1 in pulmonary sarcoidosis has previously been studied; however, the relevance of other mediators (i.e. IL-6) has not yet been evaluated. We measured the spontaneous and lipopolysaccharide (LPS)-induced release of IL-6 and tumor necrosis factor alpha (TNF alpha) by bronchoalveolar lavage cells (BAL) and peripheral blood mononuclear cells (PBMNC) in 6 control subjects (group A) and in 15 patients with sarcoidosis, 10 with active (group B), 5 with inactive disease (group C). IL-6 as well as TNF alpha were spontaneously released by BAL cells of the active group in significantly greater amounts compared to both other groups; IL-6: A, 165.5 pg/ml/24 hr/10(6) cells (range, 0-604), B, 946 (0-2467), C, 16.6 (0-83); TNF alpha: A, 162 pg/ml/24 hr/10(6) cells (0-523), B, 803 (100-17352), C, 100 (0-379). In all groups autologous PBMNC proved to be quiescent, releasing only baseline levels of the cytokines tested. After stimulation with LPS all these cells released great quantities of IL-6 and TNF alpha. In active disease a positive correlation between IL-6 and TNF alpha release was observed (r = 0.77, p < 0.02). The present study documents that in active sarcoidosis the spontaneous release of IL-6 by BAL cells parallels the spontaneous release of TNF alpha. IL-6 is capable of initiating the proliferation and activation of T cells in the lung.

Dependency on interleukin-1 of primary human in vitro T cell responses to soluble antigens

The role of interleukin (IL)-1 in antigen-specific activation of naive human T cells has been examined. Primary human T cell proliferative responses to the soluble antigen keyhole limpet hemocyanin (KLH) were decreased by neutralizing antisera to IL-1 alpha (25 +/- 7% standard error) and IL-1 beta (56 +/- 6% standard error). Inhibition by both antisera in a primary culture was usually additive. Recombinant IL-1 alpha and recombinant IL-1 beta could both re-establish responses in cultures blocked by neutralizing anti-IL-1 beta. Interestingly, the susceptibility of KLH-stimulated T cell responses to inhibition by neutralizing anti-IL-1 sera decreased with time in culture. This observation suggested that T cell responses may become less IL-1 dependent as T cells become activated or primed. In support of this notion, secondary T cell responses to purified protein derivative from Mycobacterium tuberculosis (PPD) were markedly less affected by the addition of comparable amounts of the neutralizing anti-IL-1 sera. These results demonstrate that IL-1 is one of the main co-stimulators for primary T cell activation and suggest a different requirement for IL-1 in the activation of naive compared to memory human T cells.

Impaired proliferative capacity and abnormal cytokine profile of naive and memory CD4 T cells from HIV-seropositive patients

Purified naive and memory CD4 T cells from healthy donors, HIV+ asymptomatic carriers and AIDS patients were examined for their proliferative activity and their pattern of cytokine secretion (IL-4, IL-6, interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha)) upon stimulation with phytohaemagglutinin (PHA), phorbol myristate acetate (PMA) and cross-linked anti-CD3 MoAb, in the presence of recombinant IL-2 (rIL-2). We found a decrease in the proliferative capacity of naive CD4 T cells following stimulation with PHA and PMA, and a sharp decline in this response upon cross-linked anti-CD3 stimulation in both subsets, although it predominated in the naive subpopulation. In AIDS patients, less pronounced impairment of thymidine uptake by the naive subset was found upon PHA and cross-linked anti-CD3 MoAb stimulation. In addition, an altered secretion pattern of the different cytokines was observed, consisting of abnormal secretion of IL-6 by both naive and memory cells, an abnormal pattern of IFN-gamma secretion and frequent loss of detectable IL-4 production by HIV patients. These abnormalities were even more pronounced in AIDS patients than in the asymptomatic carriers. Overall, our results extend previous reports indicating functional impairment of memory CD4 subsets in HIV+ subjects by showing that this impairment involves naive CD4 T cells.

Common Pathogenetic Pathways in Allergic and Irritant Contact Dermatitis

Despite their different pathogeneses, allergic and irritant contact dermatitis show a remarkable similarity with respect to clinical appearance, histology, and immunohistology. To further analyze this apparent contradiction, our study was designed to meticulously compare cellular infiltrates in irritant and allergic patch-test reactions by immunostaining with a broad panel of monoclonal antibodies. For this purpose, skin biopsies from allergic and irritant patch-test reactions of similar inflammatory degree were obtained from the same probands. We found that after 72 h both types of reaction were characterized by an identical dermal infiltrate consisting mainly of memory T cells, many of which were activated, and macrophages. Dermal and epidermal Langerhans cell density and HLA--DR expression of keratinocytes were also virtually identical. Our results show that antigen recognition by specific memory T cells as well as irritants can finally induce the same pattern of inflammation, including activation of T cells obviously independent of exogenous antigen.

Expression of interleukin 5 by the CD4+CD45R0+ subset of human T cells

The expression of IL5 by CD4+CD45RA+, CD4+CD45R0+ and CD3+CD8+ subsets of human peripheral blood mononuclear cells was assessed. Interleukin 5 expression was detected by RNA extraction, reverse transcription and polymerase chain reaction. Populations of highly purified cells were obtained by a protocol of sequential plastic adherence, magnetic bead separation and flow cytometric cell sorting. IL5 was clearly expressed in the CD4+CD45R0+ subset from 3 to 48 hr after activation. The CD4+CD45RA+ and CD3+CD8+ subsets expressed very much less IL5. By contrast, IL2 expression was readily detected in all sorted populations. Thus, in activated CD4+ cells, IL5 was predominantly expressed in the CD4+CD45R0+ subset, a pattern of expression corresponding to that reported for a number of other cytokines, and differing from that of IL2.

Human immunodeficiency virus type 1 envelope glycoproteins gp120 and gp160 induce interleukin-6 production in CD4+ T-cell clones

Polyclonal B-cell activation is a characteristic feature of AIDS and of the AIDS-related complex. Since the immunoregulatory cytokine interleukin-6 (IL-6) plays a major role in inducing B-cell differentiation, we examined the effects of native human immunodeficiency virus type 1 envelope glycoproteins gp120 and gp160 on IL-6 induction. In this study, we have demonstrated that both gp120 and gp160 have the ability to induce IL-6 mRNA and biologically active IL-6 protein secretion in peripheral blood mononuclear cells in vitro. The envelope protein preparations had no detectable endotoxin as tested by the Limulus amebocyte lysate assay, and hence we can rule out the effect of contaminating endotoxin, which is a potent inducer of IL-6 in monocyte/macrophage cell cultures. In addition, we have shown that the envelope glycoproteins act directly on CD4(+)-cloned T cells to induce IL-6 production in the absence of monocytes. These findings indicate that monocytes and T cells both contribute to the secretion of IL-6, which plays an important role in the pathogenesis of B-cell activation in human immunodeficiency virus infection.

Human CD4+CD45R0+ and CD4+CD45RA+ T cells synergize in response to alloantigens

Alloantigens, unlike recall antigens, activate both CD45RA+ (naive) and CD45R0+ (memory) CD4+ cells to the same extent. These T cell subsets may therefore interact with each other in response to alloantigens on transplanted grafts. We have investigated if the ability of activated CD4+CD45RA+ and CD4+CD45R0+ T cells to produce and respond to interleukin 2 (IL2) and IL4 may be involved in this interaction. After activation, both subsets up-regulate their IL2 receptor (IL2R) and IL4R expression, yet IL4 substantially enhanced the proliferation of the CD4+CD45RA+ but not of the CD4+CD45R0+ T cell subset, while IL2 increased the proliferation of CD4+CD45R0+ but not of the CD4+CD45RA+ T cells. Significantly, the CD4+CD45RA+ T cells synthesized two- to threefold more mRNA for IL2 than the CD4+CD45R0+ subset, while the CD4+CD45R0+ T cells synthesized mRNA for IL4 and interferon-gamma exclusively. The addition of IL2 to alloactivated CD4+CD45R0+ T cells further up-regulated their production of all three lymphokine mRNA; in contrast, IL4 induced an increase in mRNA for IL2 in only the alloactivated CD4+CD45RA+ subset. The reciprocity in the ability of both these CD4+ T cells to synthesize and respond to IL2 and IL4 may provide a rationale for the regulation of lymphokine interactions in vivo. Furthermore, the synergy between these subsets in response to alloantigens, which was directly quantitated by co-culturing CD4+CD45RA+ and CD4+CD45R0+ cells together prior to activation, may potentiate the alloreactivity against transplanted grafts in vivo.

A 3' splice site consensus sequence mutation in the intron 3 of the alpha-galactosidase A gene in a patient with Fabry disease

Fabry disease is an X-linked disorder accompanied with accumulation of glycosphingolipids resulting from the deficient activity of the lysosomal hydrolase, alpha-galactosidase A (alpha-GalA). In the present study, mRNA for alpha-GalA in fibroblasts from an 11-year-old Japanese patient with Fabry disease was examined using the reverse transcriptase-polymerase chain reaction (PCR). The shorter message of alpha-GalA was demonstrated in this patient when compared with the normal control. The complete deletion of exon 4 in the mRNA for alpha-GalA in the patient was disclosed by analysis of cDNA with restriction enzyme digestion and asymmetrical PCR sequencing. The direct sequencing of the genomic DNA demonstrated a single base substitution (G----A) at the 3' end of the consensus sequence of intron 3. This mutation destroyed a splice site in the alpha-GalA, which produced a mutant allele. It was also shown that the mother of the patient had this mutant as well as normal alleles as a heterozygote.

Cytokine regulation of immunoglobulin secretion by neonatal lymphocytes

In contrast to adult lymphocytes, neonatal lymphocytes secrete minimal amounts of Ig in response to stimulation with immobilized MAb to CD3. This deficiency could be overcome by the addition of supplemental IL-2, IL-4, or IL-6, resulting in the secretion of all Ig isotypes. There were no major differences in the distribution of Ig isotypes secreted in response to the cytokines alone or in combination. The Ig secreted in response to IL-4 or IL-6 was inhibited by MAb to CD25, suggesting that the effects of IL-4 and IL-6 were dependent on IL-2. Stimulation of neonatal lymphocytes with anti-CD3 was sufficient to induce expression of IL-2 receptors (CD25) on both T and B cells. IL-4 exerted direct effects on neonatal T cells by increasing IL-2 production and promoting IL-6 production by anti-CD3-stimulated neonatal lymphocytes. Antibody to IL-4 or IL-6 did not inhibit Ig secretion in response to IL-2 and antibody to IL-6 did not consistently inhibit Ig secretion in response to IL-4. Finally, in the presence of cyclosporin, anti-CD3-stimulated neonatal lymphocytes secreted Ig only with the combination of IL-2 and IL-4. These results have delineated unique, but not Ig isotype-specific, effects of cytokines in supporting Ig secretion by anti-CD3-stimulated neonatal lymphocytes. Deficient production of these cytokines is likely to contribute to the decreased capacity of neonatal lymphocytes to generate an Ig response.

Immunological memory in T cells

CD4 and CD8 T lymphocytes can be further subdivided using antibodies to isoforms of CD45 with restricted cellular distributions. These further subsets, detected in man, rodents and sheep, differ in surface phenotypes, rate of cycling, migration and response to recall antigens. Their lineage relationship has still not been fully established.

The synergy between naive and memory T cells during activation

Naive and memory T-cell subsets differ in their ability to synthesize and respond to a variety of cytokines in vitro and each subset can produce cytokines that amplify the response of the other subset. The significance of these interactions to antigen responsiveness has, until now, been unclear. In this article Arne Akbar and colleagues point out that both subsets are activated to the same extent by alloantigen and suggest that synergy may be an important event in initiating potent responses against transplanted allografts.

Signals arising from antigen-presenting cells

It has been customary to consider that antigen-presenting cells provide, in addition to the presented antigen, a second or co-stimulatory signal that leads to T-cell growth and effector function. The recent literature indicates that this two-signal notion oversimplifies the function of antigen-presenting cells. Instead it is useful to consider four groups of events: the formation of peptide-MHC complexes, the role of soluble cytokines, the action of antigen-presenting cell-T cell molecular couples distinct from the receptor for peptide MHC, and the function of antigen-presenting cells in situ.

Interleukin 6 (IL-6) and its receptor: their role in plasma cell neoplasias

Interleukin 6 (IL-6) is a multifunctional cytokine regulating immune response acute phase reaction and hematopoiesis. IL-6 plays a critical role in B cell differentiation to plasma cells and is a potent growth factor for plasmacytoma and myeloma. Abnormal production of IL-6 has been suggested to be involved in polyclonal plasma cell abnormalities and plasma cell neoplasias. The deregulated expression of the IL-6 gene in transgenic mice resulted in the generation of malignant plasmacytoma. Based on these findings, it could be considered that continuous IL-6 gene expression plays an essential role in a multistep oncogenesis of plasma cell neoplasias. The role of IL-6 and its receptor in the generation of plasma cell neoplasias and the mechanisms of the IL-6 gene expression and IL-6 receptor-mediated signal transduction are described.