Jean-Claude Lecron

Cutting edge: IL-21 is a switch factor for the production of IgG1 and IgG3 by human B cells

IL-21 is a cytokine that regulates the activation of T and NK cells and promotes the proliferation of B cells activated via CD40. In this study, we show that rIL-21 strongly induces the production of all IgG isotypes by purified CD19+ human spleen or peripheral blood B cells stimulated with anti-CD40 mAb. Moreover, it was found to specifically induce the production of IgG1 and IgG3 by CD40-activated CD19+CD27− naive human B cells. Although stimulation of CD19+ B cells via CD40 alone induced γ1 and γ3 germline transcripts, as well as the expression of activation-induced cytidine deaminase, only stimulation with both anti-CD40 mAb and rIL-21 resulted in the production of Sγ/Sμ switch circular DNA. These results show that IL-21, in addition to promoting growth and differentiation of committed B cells, is a specific switch factor for the production of IgG1 and IgG3.

Skin Inflammation Induced by the Synergistic Action of IL-17A, IL-22, Oncostatin M, IL-1α, and TNF-α Recapitulates Some Features of Psoriasis

Keratinocytes play a crucial role in the regulation of skin inflammation, responding to environmental and immune cells stimuli. They produce soluble factors that can act in an autocrine or paracrine manner on immune cells or directly on aggressors. A screening of the activities of 36 cytokines on keratinocyte gene expression identified IL-17A, IL-22, oncostatin M, TNF-α, and IL-1α as potent cytokines in inducing cutaneous inflammation. These five proinflammatory cytokines synergistically increased production of CXCL8 and β-defensin 2 (BD2). In addition, ex vivo studies on human skin explants demonstrated upregulation of BD2, S100A7, and CXCL8 expression in response to the same combination of cytokines. In vivo intradermal injection of these five cytokines in mouse increased CXCL1, CXCL2, CXCL3, S100A9, and BD3 expression, associated with neutrophil infiltration. We confirmed and extended this synergistic effect using quantitative real-time PCR analysis and observed increased expression of nine chemokines and 12 antimicrobial peptides. Production of CXCL, CXCL5, and CXCL8 by keratinocytes stimulated in the presence of this cytokine combination was associated with increased neutrophil chemotactic activity. Similarly, high production of BD2, BD3, and S100A7 was associated with an increased antimicrobial activity. Finally, the transcriptional profile observed in this in vitro model of inflammatory keratinocytes correlated with the one of lesional psoriatic skin. Our results demonstrate the important potentiating activities of IL-17A, IL-22, oncostatin M, TNF-α, and IL-1α on keratinocytes. This is particularly interesting in the context of psoriasis where these cytokines are overexpressed and could synergize to play an important role in upregulation of chemokines and antimicrobial peptides production.

Role of interleukin-6 in cardiomyocyte/cardiac fibroblast interactions during myocyte hypertrophy and fibroblast proliferation.

The process of cardiac hypertrophy is considered to involve two components: that of cardiac myocyte (CM) enlargement and cardiac fibroblast (CF) proliferation. The interleukin‐6 (IL‐6) family cytokines have been implicated in a variety of cellular and molecular interactions between myocytes and non‐myocytes (NCMs), which in turn have important roles in the development of cardiac hypertrophy. In the study of these interactions, we previously detected very high levels of IL‐6 in supernatants of a “dedifferentiated model” of adult ventricular CMs cultured with CFs. In the present study, we have used this in vitro coculture system to examine how IL‐6 is involved in the interactions between CMs and CFs during CM hypertrophy and CF proliferation. IL‐6 and its signal transducer, 130‐kDa glycoprotein (gp130), were detected by immunostaining cultured CMs and CFs with anti‐IL‐6 or anti‐gp130 antibodies. Addition of anti‐IL‐6 or anti‐gp130 antagonist antibodies into CM/CF cocultures induced a significant decrease in expression of atrial natriuretic peptide (ANP) and β‐myosin heavy chain (β‐MHC) in CMs. The presence of IL‐6 antagonist also resulted in a decrease in the surface area of 12‐day‐old CMs cultured with CFs or in the presence of fibroblast conditioned medium (FCM), and decreased fibroblast proliferation in CM/CF cocultures, particularly in the presence of a gp130 antagonist. The results also show that angiotensin II (AngII) is mainly secreted by CFs and induces IL‐6 secretion in CMs cultured with CFs or with FCM. In addition, the effects of IL‐6 on cardiomyocyte hypertrophy and fibroblast proliferation were inhibited by addition of the AT‐1 receptor antagonist, losartan. These results suggest that IL‐6 contributes significantly to CM hypertrophy by an autocrine pathway and to fibroblast proliferation by a paracrine pathway and that these effects could be mediated by AngII.

Human cardiomyocyte hypertrophy induced in vitro by gp130 stimulation

OBJECTIVES Recent in vivo and in vitro studies in animals have demonstrated that cytokines of the IL-6 family are involved in cardiac hypertrophy and in protection of cardiomyocytes against apoptosis. The present study aims to analyse the capacity of human atrial cardiac cells (i.e., cardiomyocytes and fibroblasts) to display the gp130 receptor subunit, and to evaluate its functionality. METHODS Twenty human atrial biopsies were used for immunohistochemistry, in situ hybridisation, and western blot analysis or dissociated for isolation and primary culture of cardiac cells. RESULTS Fibroblasts present in tissue or maintained in primary culture clearly express gp130 whereas the signal in cardiomyocytes is weaker. Culture of cardiac cells with a gp130 agonist antibody enhances atrial natriuretic peptide (ANP), beta myosin heavy chain (beta-MHC) expression in cardiomyocytes, and significantly increases the cell surface area microm(2)). This process could involve STAT3 (signal transducer and activator of transcription 3) phosphorylation. CONCLUSIONS These results demonstrate that gp130 activation in human cardiac cells leads to cardiomyocyte hypertrophy. We discuss several hypotheses on the role of IL-6-type cytokines on cardiomyocyte functions.

Circulating soluble gp130, soluble IL-6R, and IL-6 in patients undergoing cardiac surgery, with or without extracorporeal circulation

OBJECTIVE Soluble forms of interleukin-6 (IL-6) receptors are known to modulate biological activities of IL-6. The purpose of the study was to measure circulating levels of IL-6, sIL-6R and sgp130 in patients undergoing coronary artery bypass grafting with cardiopulmonary bypass (CPB group) or without CPB (non-CPB group). METHODS The CPB group included 19 patients and the non-CPB group 12 patients. Sera levels of IL-6, sIL-6R and sgp130 were measured by specific ELISA at the beginning of the operation (T0, 15 min before skin incision) and 6 h later (T1). RESULTS IL-6 sera levels were respectively 9+/-20 pg/ml (mean+/-SD) and 13+/-19 pg/ml at T0 and reached 340+/-250 pg/ml and 965+/-1060 pg/ml at T1 in CPB and non-CPB groups, indicating a significant increase from T0 to T1, but no differences between the two groups. When compared to T0 values, sgp130 levels decreased in both groups (respectively 105+/-37 and 115+/-35 ng/ml at T0 for CPB and non-CPB groups, and 72+/-25 and 84+/-29 ng/ml at T1) while we are not able to detect differences between the groups. Whatever the group or the time, sIL-6R concentrations remained unchanged. CONCLUSIONS We showed that the increase of IL-6 after artery bypass grafting was similar between patients operated with CPB or without CPB. We conclude that the main inductor of IL-6 release is linked to surgical trauma rather than a reaction to CPB. Since it is known that gp130 inhibits IL-6-biological activities, we suggest that the decrease of sgp130 sera levels could further enhance the inflammatory effects of IL-6 in cardiac surgery.

Keratinocytes under Fire of Proinflammatory Cytokines: Bona Fide Innate Immune Cells Involved in the Physiopathology of Chronic Atopic Dermatitis and Psoriasis

Cutaneous homeostasis and defenses are maintained by permanent cross-talk among particular epidermal keratinocytes and immune cells residing or recruited in the skin, through the production of cytokines. If required, a coordinated inflammatory response is triggered, relayed by specific cytokines. Due to numerous reasons, troubles in the resolution of this phenomenon could generate a cytokine-mediated vicious circle, promoting skin chronic inflammation, the most common being atopic dermatitis and psoriasis. In this paper, we discuss the biological effects of cytokine on keratinocytes, more particularly on specific or shared cytokines involved in atopic dermatitis or psoriasis. We report and discuss monolayer or 3D in vitro models of keratinocytes stimulated by specific sets of cytokines to mimic atopic dermatitis or psoriasis. IL-22, TNFa, IL-4, and IL-13 combination is able to mimic an “atopic dermatitis like” state. In psoriasis lesions, over expression of IL-17 is observed whereas IL-4 and IL-13 were not detected; the replacement of IL-4 and IL-13 by IL-17 from this mix is able to mimic in vitro a “psoriasis like” status on keratinocytes. We conclude that specific cytokine environment deregulation plays a central role on skin morphology and innate immunity, moving towards specific pathologies and opening the way to new therapeutic strategies.

Familial Mediterranean Fever: association of elevated IgD plasma levels with specific MEFV mutations

Familial Mediterranean Fever (FMF) is a recessively inherited disorder, characterized by episodic fever, abdominal and arthritic pain, as well as other forms of inflammation. Some FMF patients present higher IgD serum levels, and it is not yet known whether such an elevation is related to specific genotypes or correlated with a specific phenotype. In order to evaluate the association between known FMF-related mutations and IgD levels in confirmed patients, as well as the correlation between those levels and the presence of specific clinical signs, genotypic analysis and IgD plasma measurements were performed for 148 Lebanese and Jordanian FMF patients. Most common mutational patterns were M694V heterozygotes (19%) and homozygotes (17%), and V726A heterozygotes (18%) and homozygotes (5%), with an additional 11% combining both mutations. Twenty-one patients had higher IgD levels (superior to 100 μg/ml). The risk for higher IgD levels was significantly associated with M694V homozygote status (OR = 6.25) but not with heterozygotic one (OR = 1). Similarly, the risk for higher IgD was also found with V726A homozygotes (OR = 2.2) but not with heterozygotes (OR = 1.05). The use of colchicine was not statistically associated with IgD levels. Clinically, hyper IgD was also found significantly associated with arthritis (OR = 18). Thus, homozygotic status for M694V, and to a lesser extent V726A, is associated with increased risk for higher IgD plasma levels, regardless of colchicine use. Elevated IgD plasma levels are also correlated with the severity of FMF manifestations, and especially with arthritis.

Specific increase in caspase-1 activity and secretion of IL-1 family cytokines: a putative link between mevalonate kinase deficiency and inflammation

The mevalonate kinase deficiency (MKD), including hyperimmunoglobulinemia D periodic fever syndrome (HIDS) and the more severe mevalonic aciduria are rare, autosomal recessive, autoinflammatory diseases belonging to the hereditary periodic fever (HPF) family. Other members include: familial mediterranean fever (FMF), the cryopyrin-associated periodic syndromes (CAPS) and TNFR-associated periodic syndromes (TRAPS). MKD is caused by mutations in the gene encoding mevalonate kinase (MK), an enzyme of the cholesterol pathway, leading to its inactivation. The molecular mechanisms linking MKD and abnormalities of isoprenoid biosynthesis to cytokine production and inflammation have yet to be fully elucidated. Statins, which are extensively prescribed for lowering cholesterol, are potent inhibitors of 3-hydroxy-3-methylglutaryl-CoA reductase, the enzyme directly upstream of MK. In this review, we discuss recent reports demonstrating that in vitro inhibition of the mevalonate pathway by statins specifically increases the production, by activated monocytes, of cytokines of the IL-1 family, by enhancing caspase-1 activity, the enzyme responsible for IL-1beta and IL-18 maturation. The molecular mechanisms involve geranylgeranylation and the enhancement of the activity of G proteins such as Rac-1. Interestingly, activated fibroblasts from MKD patients secrete more IL-1beta than fibroblasts from healthy donors. Taken together, these data highlight the specific enhancement of the IL-1 family of cytokines, the maturation of which is caspase-1-dependent in MKD. Finally, the spectacular decrease in febrile attacks in patients with severe HIDS under IL-1 receptor antagonist (anakinra) treatment, reinforces this hypothesis. Deregulated caspase-1 activation could be responsible for the inflammatory component of MKD, thereby mechanistically linking MKD to FMF and CAPS through cytokines of the IL-1 family.

Endotoxin tolerance enhances interleukin-10 renal expression and decreases ischemia-reperfusion renal injury in rats.

ABSTRACT The potential implication of interleukin (IL) 6, tumor necrosis factor &agr; (TNF-&agr;), and IL-10 in the protective effect of low-dose lipopolysaccharide (LPS) administration against renal ischemia-reperfusion injury was evaluated in a rat model. Eighteen male Sprague-Dawley rats were injected intravenously with either 0.5 mg/kg of LPS (tolerant group) or saline (control group) 2 days before surgery. Ischemic renal injury was induced by clamping the left renal artery for 60 min on rats immediately after right-side nephrectomy. Reperfusion was obtained by clamp removal and was studied at R0 (no reperfusion), 2H (R2), and 24H (R24) by renal tubular disorder characterization and by plasma creatinine as well as renal cytokine (IL-6, IL-10, and TNF-&agr;) studies. No differences were observed between the two groups as concerns the period immediately after renal ischemia (R0). The endotoxin-tolerant group was associated with a significantly lower creatinine level at R24 (231 ± 28 vs 315 ± 36 &mgr;mol/L; P = 0.007). Pretreatment with LPS significantly reduced the degree of proximal tubule necrosis and outer medulla congestion. In such tolerant animals, renal IL-6 production was decreased, whereas IL-10 production was significantly increased at R2 and R24. There were no differences in TNF-&agr; renal production. In this study, we demonstrated that administration of low doses of LPS to rats had a protective effect from renal reperfusion injury, and our data suggest that IL-10 might play a role in this phenomenon.

Distinct Expression of IL‐36α, β, γ, their antagonist IL‐36Ra and IL‐38 in psoriasis, rheumatoid arthritis and Crohn's disease

Interleukin (IL)‐36α, IL‐36β and IL‐36γ are expressed highly in skin and are involved in the pathogenesis of psoriasis, while the antagonists IL‐36Ra or IL‐38, another potential IL‐36 inhibitor, limit uncontrolled inflammation. The expression and role of IL‐36 cytokines in rheumatoid arthritis (RA) and Crohns disease (CD) is currently debated. Here, we observed that during imiquimod‐induced mouse skin inflammation and in human psoriasis, expression of IL‐36α, γ and IL‐36Ra, but not IL‐36β and IL‐38 mRNA, was induced and correlated with IL‐1β and T helper type 17 (Th17) cytokines (IL‐17A, IL‐22, IL‐23, CCL20). In mice with collagen‐induced arthritis and in the synovium of patients with RA, IL‐36α, β, γ, IL‐36Ra and IL‐38 were all elevated and correlated with IL‐1β, CCL3, CCL4 and macrophage colony‐stimulating factor (M‐CSF), but not with Th17 cytokines. In the colon of mice with dextran sulphate sodium‐induced colitis and in patients with CD, only IL‐36α, γ and IL‐38 were induced at relatively low levels and correlated with IL‐1β and IL‐17A. We suggest that only a minor subgroup of patients with RA (17–29%) or CD (25%) had an elevated IL‐36 agonists/antagonists ratio, versus 93% of patients with psoriasis. By immunohistochemistry, IL‐36 cytokines were produced by various cell types in skin, synovium and colonic mucosa such as keratinocytes, CD68+ macrophages, dendritic/Langerhans cells and CD79α+ plasma cells. In primary cultures of monocytes or inflammatory macrophages (M1), IL‐36β and IL‐36Ra were produced constitutively, but IL‐36α, γ and IL‐38 were produced after lipopolysaccharide stimulation. These distinct expression profiles may help to explain why only subgroups of RA and CD patients have a potentially elevated IL‐36 agonists/antagonists ratio.