p21waf1/CIP1, a CDK inhibitor and a negative feedback system that controls macrophage activation

p21^WAF1/CIP1 (p21) is a crucial CDK inhibitor that controls the cell cycle. This molecule is also involved in the regulation of apoptosis and gene expression. However, like many other cell regulators, the functional activity of p21 depends on its cellular context and is controlled through phosphorylation and protein–protein interactions. p21 is also important in cells of the immune system regulating the cell cycle and preventing apoptosis of macrophages. In this issue of the European Journal of Immunology, two reports investigate the role of p21 further determining its critical role as a negative regulator of macrophage activation, in particular inhibiting the LPS‐dependent induction of TNF‐α and IL‐1β. The inhibition mediated by p21 is shown to be related to NF‐κB activity. Furthermore, the observation that p21^?/? mice are more susceptible to septic shock supports the notion that p21 is a negative regulator of macrophage activation and therefore a potential new target to control inflammatory diseases.     

IL‐1β activation in response to Staphylococcus aureus lung infection requires inflammasome‐dependent and independent mechanisms

Maintaining balanced levels of IL‐1β is extremely important to avoid host tissue damage during infection. Our goal was to understand the mechanisms behind the reduced pathology and decreased bacterial burdens in Ifnlr1^?/? mice during lung infection with Staphylococcus aureus. Intranasal infection of Ifnlr1^?/? mice with S. aureus led to significantly improved bacterial clearance, survival and decrease of proinflammatory cytokines in the airway including IL‐1β. Ifnlr1^?/? mice treated with recombinant IL‐1β displayed increased bacterial burdens in the airway and lung. IL‐1β levels in neutrophils from Ifnlr1^?/? infected mice lungs were decreased when compared to neutrophils from WT mice. Mice lacking NLRP3 and caspase‐1 had reduced IL‐1β levels 4 h after infection, due to reductions or absence of active caspase‐1 respectively, but levels at 24 h were comparable to WT infected mice. Ifnlr1^?/? infected mice had decreases in both active caspase‐1 and neutrophil elastase indicating an important role for the neutrophil serine protease in IL‐1β processing. By inhibiting neutrophil elastase, we were able to decrease IL‐1β levels by 39% in Nlrp3^?/? infected mice when compared to WT mice. These results highlight the crucial role of both proteases in IL‐1β processing, via inflammasome‐dependent and ‐independent mechanisms.     

A VLP‐based vaccine against interleukin‐1α protects mice from atherosclerosis

Interleukin (IL)‐1α is a potent proinflammatory cytokine that has been implicated in the development of atherosclerosis. We investigated whether a vaccine inducing IL‐1α neutralizing antibodies could interfere with disease progression in a murine model of atherosclerosis. We immunized Apolipoprothin E (ApoE)‐deficient mice with a vaccine (IL‐1α‐C‐Qβ) consisting of full‐length, native IL‐1α chemically conjugated to virus‐like particles derived from the bacteriophage Qβ. ApoE^?/? mice were administered six injections of IL‐1α‐C‐Qβ or nonconjugated Qβ over a period of 160 days while being maintained on a western diet. Atherosclerosis was measured in the descending aorta and in cross‐sections at the aortic root. Macrophage infiltration in the aorta was measured using CD68. Expression levels of VCAM‐1, ICAM‐1, and MCP‐1 were quantified by RT‐PCR. Immunization against IL‐1α reduced plaque progression in the descending aorta by 50% and at the aortic root by 37%. Macrophage infiltration in the aorta was reduced by 22%. Inflammation was also reduced in the adventitia, with a decrease of 54% in peri‐aortic infiltrate score and reduced expression levels of VCAM‐1 and ICAM‐1. Active immunization targeting IL‐1α reduced both the inflammatory reaction in the plaque as well as plaque progression. In summary, vaccination against IL‐1α protected ApoE^?/? mice against disease, suggesting that this may be a potential treatment option for atherosclerosis.     

Increased ILC3s associated with higher levels of IL‐1β aggravates inflammatory arthritis in mice lacking phagocytic NADPH oxidase

The role of redox regulation in immune‐mediated arthritis has been previously described. However, the relationship between innate immune cells, including innate lymphoid cells (ILCs) and phagocyte‐derived ROS, in this process remains unclear. Here, we characterize ILCs and measure the IL‐1 family cytokines along with other cytokines relevant to ILC functions and development in serum‐induced arthritic joints in wild type and phagocytic NADPH oxidase (NOX2)‐deficient Ncf1^?/? mice. We found more severe serum‐induced joint inflammation and increased NCR⁺ ILC3s in inflamed joints of Ncf1^?/? mice. Furthermore, in vitro stimulation with IL‐1β on Tbet⁺ ILC1s from joints facilitated their differentiation into ROR‐γt⁺ ILC3s. Moreover, treatment with IL‐1 antagonists effectively lowered the proportions of NCR⁺ ILC3s and IL‐17A producing ILC3s in Ncf1^?/? arthritic mice and ameliorated the joint inflammation. These results suggest that NOX2 is an essential regulator of ILC transdifferentiation and may mediate this process in a redox‐dependent manner through IL‐1β production in the inflammatory joint. Our findings shed important light on the role of ILCs in the initiation and progression in tissue inflammation and delineate a novel innate immune cell‐mediated pathogenic mechanism through which redox regulation may determine the direction of immune responses in joints.     

NTPDase1 governs P2X7‐dependent functions in murine macrophages

P2X₇ receptor is an adenosine triphosphate (ATP)‐gated ion channel within the multiprotein inflammasome complex. Until now, little is known about regulation of P2X₇ effector functions in macrophages. In this study, we show that nucleoside triphosphate diphosphohydrolase 1 (NTPDase1)/CD39 is the dominant ectonucleotidase expressed by murine peritoneal macrophages and that it regulates P2X₇‐dependent responses in these cells. Macrophages isolated from NTPDase1‐null mice (Entpd1^?/?) were devoid of all ADPase and most ATPase activities when compared with WT macrophages (Entpd1^+/+). Entpd1^?/? macrophages exposed to millimolar concentrations of ATP were more susceptible to cell death, released more IL‐1β and IL‐18 after TLR2 or TLR4 priming, and incorporated the fluorescent dye Yo‐Pro‐1 more efficiently (suggestive of increased pore formation) than Entpd1^+/+ cells. Consistent with these observations, NTPDase1 regulated P2X₇‐associated IL‐1β release after synthesis, and this process occurred independently of, and prior to, cytokine maturation by caspase‐1. NTPDase1 also inhibited IL‐1β release in vivo in the air pouch inflammatory model. Exudates of LPS‐injected Entpd1^?/? mice had significantly higher IL‐1β levels when compared with Entpd1^+/+ mice. Altogether, our studies suggest that NTPDase1/CD39 plays a key role in the control of P2X₇‐dependent macrophage responses.     

Card9‐dependent IL‐1β regulates IL‐22 production from group 3 innate lymphoid cells and promotes colitis‐associated cancer

Inflammatory bowel diseases (IBD) are key risk factors for the development of colorectal cancer, but the mechanisms that link intestinal inflammation with carcinogenesis are insufficiently understood. Card9 is a myeloid cell‐specific signaling protein that regulates inflammatory responses downstream of various pattern recognition receptors and which cooperates with the inflammasomes for IL‐1β production. Because polymorphisms in Card9 were recurrently associated with human IBD, we investigated the function of Card9 in a colitis‐associated cancer (CAC) model. Card9^?/? mice develop smaller, less proliferative and less dysplastic tumors compared to their littermates and in the regenerating mucosa we detected dramatically impaired IL‐1β generation and defective IL‐1β controlled IL‐22 production from group 3 innate lymphoid cells. Consistent with the key role of immune‐derived IL‐22 in activating STAT3 signaling during normal and pathological intestinal epithelial cell (IEC) proliferation, Card9^?/? mice also exhibit impaired tumor cell intrinsic STAT3 activation. Our results imply a Card9‐controlled, ILC3‐mediated mechanism regulating healthy and malignant IEC proliferation and demonstrates a role of Card9‐mediated innate immunity in inflammation‐associated carcinogenesis.     

SQSTM1/p62/A170 regulates the severity of Legionella pneumophila pneumonia by modulating inflammasome activity

Sequestosome1/A170/p62 (SQSTM1) is a scaffold multifunctional protein involved in several cellular events, such as signal transduction, cell survival, cell death, and inflammation. SQSTM1 expression by macrophages is induced in response to environmental stresses; however, its role in macrophage‐mediated host responses to environmental stimuli, such as infectious pathogens, remains unclear. In this study, we investigated the role of SQSTM1 in host responses to Legionella pneumophila, an intra‐cellular pathogen that infects macrophages, in both an SQSTM1‐deficient (SQSTM1^?/?) mouse model and macrophages from these mice. Compared with wild‐type (WT) macrophages, the production and secretion of the proinflammatory cytokine IL‐1β was significantly enhanced in SQSTM1^?/? macrophages after infection with L. pneumophila. Inflammasome activity, indicated by the level of IL‐18 and caspase‐1 activity, was also elevated in SQSTM1^?/? macrophages after infection with L. pneumophila. SQSTM1 may interact with nucleotide‐binding oligomerization domain‐like receptor family, caspase recruitment domain‐containing 4 and nucleotide‐binding oligomerization domain like receptor family, pyrin domain containing 3 proteins to inhibit their self‐dimerization. Acute pulmonary inflammation induced by L. pneumophila and silica was enhanced in SQSTM1^?/? mice with an increase in IL‐1β levels in the bronchoalveolar lavage fluids. These findings suggest that SQSTM1 is a negative regulator of acute pulmonary inflammation, possibly by regulating inflammasome activity and subsequent proinflammatory cytokine production.     

IL‐37 Expression is Upregulated in Patients with Tuberculosis and Induces Macrophages Towards an M2‐like Phenotype

Interleukin‐37 (IL‐37), a member of the IL‐1 family, primarily functions as an anti‐inflammatory cytokine, reducing inflammation and suppressing the immune response. However, the expression and role of IL‐37 in tuberculosis (TB) remains unknown. We aimed to measure serum levels of IL‐37 and several important cytokines in 25 patients with active TB and to analyse their association with disease activity. We found that IL‐37 levels decreased in patients with TB and recovered after treatment. IL‐37 levels negatively correlated with the serum concentration of IFN‐γ and IL‐12 but positively correlated with IL‐10 and TGF‐β levels. After IL‐37, secretion was blocked in peripheral blood mononuclear cells from active patients with TB, IFN‐γ and IL‐10 production was significantly upregulated; this was not observed in healthy donors or patients after treatment. IL‐37 knockdown significantly enhanced the phagocytic activity of THP1‐derived macrophages towards Mycobacterium tuberculosis (M. tb). M1/M2 polarization‐associated markers were detected simultaneously, and IL‐37 induced a phenotypic shift in THP1‐derived macrophages towards a high CD206⁺ and low CD86⁺ macrophage subtype. Furthermore, this phenotypic shift was accompanied by upregulated mRNA levels of arginase 1, TGF‐β and IL‐10, which are characteristic hallmarks of M2 macrophages. In conclusion, our results suggest that increased levels of IL‐37 in patients with TB are associated with IFN‐γ, IL‐12, IL‐10 and TGF‐β levels and that IL‐37 plays a pathological role in TB infection by inhibiting the production of pro‐inflammatory cytokines and inducing macrophages towards an M2‐like phenotype. Thus, IL‐37 may be a novel research target to understand the pathogenesis of TB infection.     

Enhanced protection from fibrosis and inflammation in the combined absence of IL‐13 and IFN‐γ

Persistent or dysregulated IL‐13 responses are key drivers of fibrosis in multiple organ systems, and this identifies this cytokine as an important therapeutic target. Nevertheless, the mechanisms by which IL‐13 blockade leads to the amelioration of fibrosis remain unclear. Because IFN‐γ exhibits potent anti‐fibrotic activity, and IL‐4Rα signalling antagonizes IFN‐γ effector function, compensatory increases in IFN‐γ activity following IL‐13/IL‐4Rα blockade might contribute to the reduction in fibrosis. To investigate the role of IFN‐γ, we developed novel IL‐13^?/?/IFN‐γ^?/? double cytokine‐deficient mice and examined disease progression in models of type 2‐driven fibrosis. As predicted, we showed that fibrosis in the lung and liver are both highly dependent on IL‐13. We also observed increased IFN‐γ production and inflammatory activity in the tissues of IL‐13‐deficient mice. Surprisingly, however, an even greater reduction in fibrosis was observed in IL‐13/IFN‐γ double deficient mice, most notably in the livers of mice chronically infected with Schistosoma mansoni. The increased protection was associated with marked decreases in Tgfb1, Mmp12, and Timp1 mRNA expression in the tissues; reduced inflammation; and decreased expression of important pro‐inflammatory mediators such as TNF‐α. Experiments conducted with neutralizing monoclonal antibodies to IL‐13 and IFN‐γ validated the findings with the genetically deficient mice. Together, these studies demonstrate that the reduction in fibrosis observed when IL‐13 signalling is suppressed is not dependent on increased IFN‐γ activity. Instead, by reducing compensatory increases in type 1‐associated inflammation, therapeutic strategies that block IFN‐γ and IL‐13 activity simultaneously can confer greater protection from progressive fibrosis than IL‐13 blockade alone. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.     

Protein tyrosine phosphatase PTPN22 regulates IL‐1β dependent Th17 responses by modulating dectin‐1 signaling in mice

A single nucleotide polymorphism within the PTPN22 gene is a strong genetic risk factor predisposing to the development of multiple autoimmune diseases. PTPN22 regulates Syk and Src family kinases downstream of immuno‐receptors. Fungal β‐glucan receptor dectin‐1 signals via Syk, and dectin‐1 stimulation induces arthritis in mouse models. We investigated whether PTPN22 regulates dectin‐1 dependent immune responses. Bone marrow derived dendritic cells (BMDCs) generated from C57BL/6 wild type (WT) and Ptpn22^?/? mutant mice, were pulsed with OVA_323‐339 and the dectin‐1 agonist curdlan and co‐cultured in vitro with OT‐II T‐cells or adoptively transferred into OT‐II mice, and T‐cell responses were determined by immunoassay. Dectin‐1 activated Ptpn22^?/? BMDCs enhanced T‐cell secretion of IL‐17 in vitro and in vivo in an IL‐1β dependent manner. Immunoblotting revealed that compared to WT, dectin‐1 activated Ptpn22^?/? BMDCs displayed enhanced Syk and Erk phosphorylation. Dectin‐1 activation of BMDCs expressing Ptpn22^R619W (the mouse orthologue of human PTPN22^R620W) also resulted in increased IL‐1β secretion and T‐cell dependent IL‐17 responses, indicating that in the context of dectin‐1 Ptpn22^R619W operates as a loss‐of‐function variant. These findings highlight PTPN22 as a novel regulator of dectin‐1 signals, providing a link between genetically conferred perturbations of innate receptor signaling and the risk of autoimmune disease.     

Lipocalin‐2 ensures host defense against Salmonella Typhimurium by controlling macrophage iron homeostasis and immune response

Lipocalin‐2 (Lcn2) is an innate immune peptide with pleiotropic effects. Lcn2 binds iron‐laden bacterial siderophores, chemo‐attracts neutrophils and has immunomodulatory and apoptosis‐regulating effects. In this study, we show that upon infection with Salmonella enterica serovar Typhimurium, Lcn2 promotes iron export from Salmonella‐infected macrophages, which reduces cellular iron content and enhances the generation of pro‐inflammatory cytokines. Lcn2 represses IL‐10 production while augmenting Nos2, TNF‐α, and IL‐6 expression. Lcn2^?/? macrophages have elevated IL‐10 levels as a consequence of increased iron content. The crucial role of Lcn‐2/IL‐10 interactions was further demonstrated by the greater ability of Lcn2^?/? IL‐10^?/? macrophages and mice to control intracellular Salmonella proliferation in comparison to Lcn2^?/? counterparts. Overexpression of the iron exporter ferroportin‐1 in Lcn2^?/? macrophages represses IL‐10 and restores TNF‐α and IL‐6 production to the levels found in wild‐type macrophages, so that killing and clearance of intracellular Salmonella is promoted. Our observations suggest that Lcn2 promotes host resistance to Salmonella Typhimurium infection by binding bacterial siderophores and suppressing IL‐10 production, and that both functions are linked to its ability to shuttle iron from macrophages.     

Distinct expression of interleukin (IL)‐36α, β and 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 Crohn's 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.     

Synovial macrophage‐derived IL‐1β regulates the calcitonin receptor in osteoarthritic mice

Recent studies have reported that calcitonin gene‐related peptide (CGRP) contributes to joint pain. However, regulation of the CGRP/CGRP receptor signalling in osteoarthritis (OA) is not fully understood. To investigate the regulation of CGRP/CGRP receptor signalling by macrophages in the synovial tissue (ST) of OA joints, we characterized the gene expression profiles of CGRP and CGRP receptors in the ST of OA mice (STR/Ort). In addition, we examined whether macrophage depletion by the systemic injection of clodronate‐laden liposomes affected the expression of CGRP and CGRP receptors in ST. CD11c⁺ macrophages in the ST of STR/Ort and C57BL/6J mice were analysed by flow cytometry. Real‐time polymerase chain reaction (PCR) was used to evaluate the expression of interleukin (IL)‐1β, CGRP, calcitonin receptor‐like receptor (CLR) and receptor activity‐modifying protein 1 (RAMP1) in F4/80⁺ and F4/80^? cells. The effects of IL‐1β on the expression of CGRP and CLR by cultured synovial cells were also examined. The percentage of CD11c⁺ macrophages in the ST of STR/Ort was higher than that in C57/BL6J mice. Notably, the F4/80⁺ cell fraction expressed IL‐1β highly, whereas the F4/80^? cell fraction expressed CGRP, CLR, and RAMP1 highly. In addition, expression of the IL‐1β and CLR genes was increased in ST, but was decreased upon macrophage depletion, and the IL‐1β treatment of cultured synovial cells up‐regulated CLR. Taken together, the present findings suggest that synovial macrophages are the major producers of IL‐1β and regulators of CLR in OA mice. Therefore, macrophages and IL‐1β may be suitable therapeutic targets for treating OA pain.     

IL‐4 blocks M‐CSF‐dependent macrophage proliferation by inducing p21Waf1 in a STAT6‐dependent way

Macrophages are recruited from the blood stream to the inflammatory loci to carry out their functional activities. In an early phase of the cell cycle, macrophages become activated by Th1‐type cytokines (i.e. IFN‐γ), thereby producing several factors (cytokines, NO, etc.) and developing pro‐inflammatory activities. When bacteria and apoptotic bodies are removed, through the interaction with Th2‐type cytokines (i.e. IL‐4), macrophages become anti‐inflammatory and repair damaged tissues. Incubation of bone‐marrow‐derived macrophages with IFN‐γ or IL‐4 blocked their proliferation. While M‐CSF withdrawal caused cell cycle arrest at the early G₁ phase, treatment of macrophages with IFN‐γ or IL‐4 caused this arrest later, at the G₁/S boundary. Proliferation arrest was not due to an induction of apoptosis. IFN‐γ and IL‐4 induced the expression of the cyclin‐dependent kinase (Cdk) inhibitor p21^Waf1. Using KO mice and iRNA experiments, we found that p21^Waf1is required for IL‐4‐ but not for IFN‐γ‐dependent inhibition of macrophage proliferation. IL‐4 inhibited M‐CSF‐dependent Cdk‐2 and Cdk‐4 activities, which are necessary for entry and passage through the S phase of the cell cycle. The signal transduction used to induce the expression of p21^Waf1after interaction of IL‐4 with the corresponding receptor was mediated by STAT6. Thus, IL‐4 and IFN‐γ blocked M‐CSF‐induced macrophage proliferation through distinct mechanisms.     

T‐bet protects against exacerbation of schistosome egg‐induced immunopathology by regulating Th17‐mediated inflammation

C57BL/6 mice infected with Schistosoma mansoni naturally develop mild CD4⁺ T‐cell‐mediated immunopathology characterized by small hepatic granulomas around parasite eggs. However, immunization with soluble egg Ag in CFA markedly exacerbates the lesions by inducing a potent proinflammatory environment with high levels of IFN‐γ and IL‐17, which are signature cytokines of distinct Th1‐ versus Th17‐cell lineages. To determine the relative role of these subsets in disease exacerbation, we examined mice deficient in T‐bet (T‐bet^?/?), which is required for Th1 differentiation and IFN‐γ production. We now report that immunization with soluble egg Ag in CFA caused a significantly greater enhancement of egg‐induced hepatic immunopathology in T‐bet^?/? mice compared with WT controls, and analysis of their granulomas disclosed a higher proportion of activated DC and CD4⁺ T cells, as well as a marked influx of neutrophils. The absence of IFN‐γ in the T‐bet^?/? mice correlated with a marked increase in IL‐23p19, IL‐17 and TNF‐α in granulomas and MLN. In contrast, T‐bet^?/? mice had lower levels of IL‐4, IL‐5 and IL‐10 and a reduction in FIZZ1 and FoxP3 expression, suggesting diminished regulatory activity, respectively, by alternatively activated macrophages and Treg. These findings demonstrate that T‐bet‐dependent signaling negatively regulates Th17‐mediated immunopathology in severe schistosomiasis.     

Human cathelicidin LL‐37 and its derivative IG‐19 regulate interleukin‐32‐induced inflammation

Human cathelicidin LL‐37 protects against infections and endotoxin‐induced inflammation. In a recent study we have shown that IG‐19, an LL‐37‐derived peptide, protects in a murine model of arthritis. Cytokine interleukin‐32 (IL‐32) is elevated and directly associated with the disease severity of inflammatory arthritis. Therefore, in this study we examined the effects of LL‐37 and IG‐19 on IL‐32‐induced responses in human peripheral blood‐derived mononuclear cells (PBMC) and macrophages. We showed that CD14⁺ monocytes are the primary cells that produce pro‐inflammatory tumour necrosis factor‐α (TNF‐α) following stimulation of PBMC with IL‐32. We demonstrated that LL‐37 and IG‐19 significantly suppress IL‐32‐induced production of pro‐inflammatory cytokines, e.g. TNF‐α and IL‐1β, without altering chemokine production. In contrast, LL‐37 and IG‐19 enhance the production of the anti‐inflammatory cytokine IL‐1RA. Further mechanistic studies revealed that LL‐37 and IG‐19 suppress IL‐32‐mediated phosphorylation of Fyn (Y420) Src kinase. In contrast, IL‐32‐mediated phosphorylation of AKT‐1 (T308) and MKP‐1 (S359) is not suppressed by the peptides. LL‐37 and IG‐19 alone induce the phosphorylation of MKP‐1 (S359), which is a known negative regulator of inflammation. Furthermore, the peptides induce the activity of p44/42 mitogen‐activated protein kinase, which is known to phosphorylate MKP‐1 (S359). This is the first study to demonstrate the regulation of IL‐32‐induced inflammation by LL‐37 and its derivative peptide IG‐19. The mechanistic results from this study suggest that regulation of immune‐mediated inflammation by these peptides may be controlled by the dual phosphatase MKP‐1. We speculate that LL‐37 and its derivatives may contribute to the control of immune‐mediated inflammatory diseases.