Cytosolic Nucleic Acid Sensors in Inflammatory and Autoimmune Disorders

Innate immunity employs germline-encoded pattern recognition receptors (PRRs) to sense microbial pattern molecules. Recognition of pathogen-associated molecular patterns (PAMPs) by various PPRs located on the cell membrane or in the cytosol leads to the activation of cell signaling pathways and production of inflammatory mediators. Nucleic acids including DNA, RNA, and their derivatives are potent PAMPs which can be recognized by multiple PRRs to induce inflammatory responses. While nucleic acid sensors can also sense endogenous nucleic acids, they are capable of discriminating self from non-self. However, defects in nucleic acid sensing PRRs or dysregulation of nucleic acid sensing signaling pathways may cause excessive activation of the immune system resulting in the development of inflammatory and autoimmune diseases. This review will discuss the major pathways for sensing intracellular nucleic acids and how defects in these nucleic acid sensing are associated with different kinds of autoimmune and inflammatory disorders.

NOD2 Suppresses Colorectal Tumorigenesis via Downregulation of the TLR Pathways

Although NOD2 is the major inflammatory bowel disease susceptibility gene, its role in colorectal tumorigenesis is poorly defined. Here, we show that Nod2-deficient mice are highly susceptible to experimental colorectal tumorigenesis independent of gut microbial dysbiosis. Interestingly, the expression of inflammatory genes and the activation of inflammatory pathways, including NF-κB, ERK, and STAT3 are significantly higher in Nod2^-/- mouse colons during colitis and colorectal tumorigenesis, but not at homeostasis. Consistent with higher inflammation, there is greater proliferation of epithelial cells in hyperplastic regions of Nod2^-/- colons. In vitro studies demonstrate that, while NOD2 activates the NF-κB and MAPK pathways in response to MDP, it inhibits TLR-mediated activation of NF-κB and MAPK. Notably, NOD2-mediated downregulation of NF-κB and MAPK is associated with the induction of IRF4. Taken together, NOD2 plays a critical role in the suppression of inflammation and tumorigenesis in the colon via downregulation of the TLR signaling pathways.

Pomalidomide, bortezomib and low-dose dexamethasone in lenalidomide-refractory and proteasome inhibitor-exposed myeloma

This phase 1 dose-escalation study evaluated pomalidomide, bortezomib (subcutaneous (SC) or intravenous (IV)) and low-dose dexamethasone (LoDEX) in lenalidomide-refractory and proteasome inhibitor-exposed relapsed or relapsed and refractory multiple myeloma (RRMM). In 21-day cycles, patients received pomalidomide (1-4 mg days 1-14), bortezomib (1-1.3 mg/m2 days 1, 4, 8 and 11 for cycles 1-8; days 1 and 8 for cycle ⩾9) and LoDEX. Primary endpoint was to determine the maximum tolerated dose (MTD). Thirty-four patients enrolled: 12 during escalation, 10 in the MTD IV bortezomib cohort and 12 in the MTD SC bortezomib cohort. Patients received a median of 2 prior lines of therapy; 97% bortezomib exposed. With no dose-limiting toxicities, MTD was defined as the maximum planned dose: pomalidomide 4 mg, bortezomib 1.3 mg/m2 and LoDEX. All patients discontinued treatment by data cutoff (2 April 2015). The most common grade 3/4 treatment-emergent adverse events were neutropenia (44%) and thrombocytopenia (26%), which occurred more frequently with IV than SC bortezomib. No grade 3/4 peripheral neuropathy or deep vein thrombosis was reported. Overall response rate was 65%. Median duration of response was 7.4 months. Pomalidomide, bortezomib and LoDEX was well tolerated and effective in lenalidomide-refractory and bortezomib-exposed patients with RRMM.

The DNA Sensor AIM2 Maintains Intestinal Homeostasis via Regulation of Epithelial Antimicrobial Host Defense

Microbial pattern molecules in the intestine play immunoregulatory roles via diverse pattern recognition receptors. However, the role of the cytosolic DNA sensor AIM2 in the maintenance of intestinal homeostasis is unknown. Here, we show that Aim2(-/-) mice are highly susceptible to dextran sodium sulfate-induced colitis that is associated with microbial dysbiosis as represented by higher colonic burden of commensal Escherichia coli. Colonization of germ-free mice with Aim2(-/-) mouse microbiota leads to higher colitis susceptibility. In-depth investigation of AIM2-mediated host defense responses reveals that caspase-1 activation and IL-1β and IL-18 production are compromised in Aim2(-/-) mouse colons, consistent with defective inflammasome function. Moreover, IL-18 infusion reduces E. coli burden as well as colitis susceptibility in Aim2(-/-) mice. Altered microbiota in inflammasome-defective mice correlate with reduced expression of several antimicrobial peptides in intestinal epithelial cells. Together, these findings implicate DNA sensing by AIM2 as a regulatory mechanism for maintaining intestinal homeostasis.

The NLRP12 Sensor Negatively Regulates Autoinflammatory Disease by Modulating Interleukin-4 Production in T Cells

Missense mutations in the nucleotide-binding oligomerization domain (NOD)-like receptor pyrin domain containing family of gene 12 (Nlrp12) are associated with periodic fever syndromes and atopic dermatitis in humans. Here, we have demonstrated a crucial role for NLRP12 in negatively regulating pathogenic T cell responses. Nlrp12(-/-) mice responded to antigen immunization with hyperinflammatory T cell responses. Furthermore, transfer of CD4(+)CD45RB(hi)Nlrp12(-/-) T cells into immunodeficient mice led to more severe colitis and atopic dermatitis. NLRP12 deficiency did not, however, cause exacerbated ascending paralysis during experimental autoimmune encephalomyelitis (EAE); instead, Nlrp12(-/-) mice developed atypical neuroinflammatory symptoms that were characterized by ataxia and loss of balance. Enhanced T-cell-mediated interleukin-4 (IL-4) production promotes the development of atypical EAE disease in Nlrp12(-/-) mice. These results define an unexpected role for NLRP12 as an intrinsic negative regulator of T-cell-mediated immunity and identify altered NF-κB regulation and IL-4 production as key mediators of NLRP12-associated disease.

Drak2 is not required for tumor surveillance and suppression

Drak2 is a promising therapeutic target to treat organ-specific autoimmune diseases such as type 1 diabetes and multiple sclerosis without causing generalized immune suppression. Inhibition of Drak2 may also prevent graft rejection following organ transplantation. However, Drak2 may function as a critical tumor suppressor, which would challenge the prospect of targeting Drak2 for therapeutic treatment. Thus, we examined the susceptibility of Drak2 (-/-) mice in several tumor models. We show that Drak2 is not required to prevent tumor formation in a variety of settings. Therefore, Drak2 does not function as an essential tumor suppressor in in vivo tumor models. These data further validate Drak2 as a viable therapeutic target to treat autoimmune disease and graft rejection. Importantly, these data also indicate that while Drak2 may induce apoptosis when overexpressed in cell lines, it is not an essential tumor suppressor.

Role of inflammasomes in host defense against Citrobacter rodentium infection

Citrobacter rodentium is an enteric bacterial pathogen of the mouse intestinal tract that triggers inflammatory responses resembling those of humans infected with enteropathogenic and enterohemorrhagic Escherichia coli. Inflammasome signaling is emerging as a central regulator of inflammatory and host responses to several pathogens, but the in vivo role of inflammasome signaling in host defense against C. rodentium has not been characterized. Here, we show that mice lacking the inflammasome components Nlrp3, Nlrc4, and caspase-1 were hypersusceptible to C. rodentium-induced gastrointestinal inflammation. This was due to defective interleukin (IL)-1β and IL-18 production given that il-1β(-/-) and il-18(-/-) mice also suffered from increased bacterial burdens and exacerbated histopathology. C. rodentium specifically activated the Nlrp3 inflammasome in in vitro-infected macrophages independently of a functional bacterial type III secretion system. Thus, production of IL-1β and IL-18 downstream of the Nlrp3 and Nlrc4 inflammasomes plays a critical role in host defense against enteric infections caused by C. rodentium.

Inflammasomes and Intestinal Tumorigenesis

Colorectal cancer is a major health problem in developed countries. Chronic intestinal inflammation predisposes individuals to the development of colorectal cancer. The intracellular NOD-like receptors (NLRs) have emerged as crucial regulators of intestinal inflammation and colorectal tumorigenesis. Activation of several NLRs leads to the formation of a protein complex called the inflammasome, which then triggers the activation of the cysteine protease caspase-1 and the downstream maturation and secretion of the inflammatory cytokines interleukin-1β and -18. Defective inflammasome signaling in the gut contributes to colitis and colorectal tumorigenesis by increasing the permeability of the epithelial barrier, dysregulating the proliferation of epithelial cells, and inducing oncogenic mediators. In this review, we discuss our current knowledge on how the inflammasome protects against colorectal tumorigenesis.

The Nlrp3 inflammasome: contributions to intestinal homeostasis

Inflammatory bowel diseases (IBD) such as Crohn's disease and ulcerative colitis constitute a major health problem in developed countries. Moreover, IBD predisposes to the development of colorectal cancer. The intracellular NOD-like receptor Nlrp3 is rapidly emerging as a crucial regulator of intestinal homeostasis. This innate immune receptor mediates assembly of the inflammasome complex in the presence of microbial ligands, triggering caspase-1 activation and secretion of IL-1β and IL-18. Recent studies suggest that defective Nlrp3 inflammasome signaling in the gut contributes to IBD through increased permeability across the epithelial barrier and the induction of detrimental immune responses against invading commensals. Here, we review and discuss recent advances of the role of the Nlrp3 inflammasome in colitis and colon tumorigenesis.

[New paradigm of host defense against intracellular pathogens by nitric oxide]

Nitric oxide (NO) produced by inducible NO synthase (iNOS) during infection plays a crucial role in host defense mechanisms, via its antimicrobial and cytoprotective activities. Infection of Salmonella typhimurium in mice induces excessive production of NO, as a host defense response. We found much greater bacterial growth and apoptotic changes in iNOS-deficient (iNOS-/-) mice than in wild-type mice. However, the mechanism of NO-mediated cytoprotection during Salmonella infection remained unclear. An important signaling mechanism induced by NO is heme oxygenase (HO)-1, a significant cytoprotective molecule produced by oxidative stress. Thus, we sought to clarify NO-dependent cytoprotective and antimicrobial host defense, with a particular focus on the signaling mechanism of HO-1 induction. We recently discovered a nitrated cyclic nucleotide, 8-nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP), which is formed via NO possibly with reactive oxygen species. We observed strong immunoreactivity for 8-nitro-cGMP in Salmonella-infected wild-type mouse liver and peritoneal macrophages in culture but not in iNOS-/- mouse liver and macrophages. Moreover, a higher apoptosis was observed in iNOS-/- macrophages compared with wild-type macrophages after Salmonella infection, but the difference was nullified when iNOS-/- cells were treated with 8-nitro-cGMP. Finally, authentic 8-nitro-cGMP induced HO-1 in cultured macrophages infected with Salmonella. The signaling function of 8-nitro-cGMP appears to be mediated by its unique reaction with the sulfhydryl group of cysteine, thus forming a proteinS-cGMP adduct, which is an important mechanism of post-translational modification of proteins called protein S-guanylation. More importantly, we found 8-nitro-cGMP-dependent S-guanylation of Keap1, a regulatory protein of transcription factor Nrf2, which regulates the transcription of HO-1. In this review, we focus on a unique mechanism of NO-mediated host defense via formation of a novel signaling molecule, 8-nitro-cGMP in microbial infections.

The antiapoptotic effect of IL-6 autocrine loop in a cellular model of advanced prostate cancer is mediated by Mcl-1

Levels of the proinflammatory cytokine interleukin-6 (IL-6) are increased in therapy-resistant prostate cancer. IL-6 has been considered a positive growth factor in late-stage prostate cancer cells and a potential target for therapeutic interference. Effects of inhibition of IL-6 on cell survival were studied in LNCaP-IL6+ cells, a model system for advanced prostate cancer, which produce IL-6. We show that the autocrine IL-6 loop is responsible for resistance to apoptosis and increased cellular levels of myeloid cell leukemia-1 (Mcl-1) protein, an antiapoptotic member of the Bcl-2 family. Treatment of cells with a chimeric anti-IL-6 antibody (CNTO 328) led to the induction of apoptosis and downregulation of Mcl-1 protein levels. Specific knockdown of Mcl-1 gene expression by small interfering RNA also yielded an increase in apoptosis of LNCaP-IL-6+ cells. Vice versa, inactivation of IL-6 autocrine loop had no influence on apoptosis levels in the absence of Mcl-1, thus suggesting this molecule as a mediator of the survival action of IL-6. Mcl-1 protein regulation by the endogenous cytokine directly involved the extracellular signal-regulated kinase 1/2 mitogen-activated protein kinase pathway. Our data support the concept of anti-IL-6 targeted therapy in therapy-resistant prostate cancer.

Clinical cytokine network cytometry

Cytokines play an important role in human health and disease. Monitoring their effects and detecting alterations in the complex balance of cytokines within a patient will undoubtedly become increasingly common in the clinical laboratory. Because of the complexity of the network interactions, multiple assays measuring soluble cytokines ("what"), cytokine-producing cells ("who"), surface receptors ("where"), and function (how) simultaneously are necessary to provide clinically useful information. The explosion of reagents and applications for use in the clinical flow cytometry laboratory makes this the perfect setting to perform the multidimensional studies required. Clinical cytokine network cytometry exemplifies the power of multiparameter, high throughput technologies that will change the face of clinical laboratories in the twenty-first century.

The role for interleukin-12 therapy of cutaneous T cell lymphoma

Recent phase I and phase II trials using recombinant human interleukin-12 (rhIL-12) for cutaneous T cell lymphoma (CTCL) have been completed. Observations on 32 evaluable patients revealed an overall response rate approaching 50 percent. Biopsy of regressing lesions revealed an increase in numbers of CD8+ and/or TIA-1+ T cells. These results suggest that rhIL-12 may induce lesion regression by augmenting antitumor cytotoxic T cell responses. Future trials will be focused on strategies for further immune enhancement by the concomitant use of additional immune augmenting cytokines with rhIL-12.

Dysregulation of lymphocyte interleukin-12 receptor expression in Sézary syndrome

Initial phase I and II clinical trials with recombinant human interleukin-12 have demonstrated the therapeutic efficacy of this cytokine in early stage cutaneous T cell lymphoma as compared with more advanced stages such as the leukemic Sézary syndrome. In an effort to optimize the use of recombinant human interleukin-12, using flow cytometry we studied the regulation of the interleukin-12 receptor beta1 (high affinity chain) and beta2 (chain necessary for interleukin-12 signal transduction) on normal volunteer CD4+ and CD8+ T cells and CD4+ and CD8+ cells from eight patients with different degrees of leukemic involvement with Sézary syndrome. The beta1 chain was not readily detectable on resting normal and T cells from Sézary patients, but expression was induced following T cell activation with phytohemagglutinin. Similarly, the beta2 chain was not detectable on resting normal volunteer T cells, but could be induced following phytohemagglutinin stimulation. Moreover, the beta2 chain on normal volunteer T cells was markedly upregulated following short-term culture with interferon-gamma or recombinant human interleukin-12. CD8+ T cells routinely exhibited a greater expression of beta2 than did CD4+ T cells. In marked contrast, both CD4+ and CD8+ T cells from patients with Sézary syndrome and a high tumor cell burden (> 50% circulating atypical Sézary T cells) failed to express the beta2 chain under any culture conditions. Although, culture with anti-interleukin-10 also markedly increased beta2 expression on normal volunteer T cells, this failed to induce expression on either CD4+ or CD8+ T cells from Sézary patients and a high tumor burden. Investigation of patients with Sézary syndrome and a low tumor cell burden (< 15% circulating Sézary T cells) revealed a pattern of beta2 expression that was intermediate between advanced Sézary syndrome and normal volunteers. Both CD4+ and CD8+ peripheral blood T cells from these earlier stage patients were induced to express the beta2 chain, although at a lower frequency of positivity than T cells from normals, following culture with phytohemagglutinin, interferon-gamma, recombinant human interleukin-12, or anti-interleukin-10. These results indicate that short-term culture with interferon-gamma and recombinant human interleukin-12 potently upregulates beta2 chain expression on T cells from normal volunteers, whereas a similar, but less marked effect occurs on T cells from Sézary syndrome patients and a low circulating tumor cell burden. In contrast, the beta2 chain appears to be suppressed on both CD4+ and CD8+ T cells from Sézary patients with a heavy circulating tumor cell burden and it is not induced by interferon-gamma or recombinant human interleukin-12. Therefore, recombinant human interleukin-12 is likely to be most effective for early stage cutaneous T cell lymphoma due to a greater display of beta2 receptors on responding CD8+ anti-tumor cytotoxic T cells.

Chlamydia pneumoniae inhibits apoptosis in human peripheral blood mononuclear cells through induction of IL-10

Chlamydia pneumoniae is a common cause of pulmonary infection, with serum positivity in at least 50% of the general population. In this study, we report that human PBMCs exposed to C. pneumoniae are resistant to apoptosis induced by the potent photoactivated chemotherapeutic agents 8-methoxypsoralen and hypericin. In contrast, PBMCs treated with a heat-inactivated inoculum exhibit normal susceptibility to apoptosis. We also observed that human PBMCs are responsive to C. pneumoniae infection by secretion of key immune regulatory cytokines, including IL-12 and IL-10. While IL-12 may play an important role in limiting C. pneumoniae proliferation within cells, IL-10 serves an anti-inflammatory function by down-regulating proinflammatory cytokines such as IL-12 and TNF-alpha. Depletion of endogenous IL-10, but not of IL-12, abolished the apoptosis resistance of C. pneumoniae-infected PBMCs. Furthermore, addition of exogenous IL-10, but not IL-12, significantly increased the resistance of control inoculum-treated PBMCs to photoactivated 8-methoxypsoralen- and hypericin-induced apoptosis. Therefore, we conclude that C. pneumoniae possesses an antiapoptotic mechanism. The resistance to apoptosis observed in PBMCs exposed to C. pneumoniae is due, at least partially, to the IL-10 induced during C. pneumoniae infection.

Pesticides in groundwater: the aldicarb story in Suffolk County, NY

Aldicarb, a carbamate pesticide, was detected for the first time in groundwater in Suffolk County, New York, in August 1979. Although all laboratory and field studies indicated that the pesticide could not reach groundwater, a combination of circumstances allowed its residues not only to reach groundwater but also to be ingested by humans. Inquiries in hospitals and poison control centers did not reveal any cases of carbamate poisoning. The extensive monitoring program, conducted by the County in cooperation with the federal and state agencies and the Union Carbide Corporation, showed that 1,121 (13.5 per cent) of the 8,404 wells examined exceeded the state recommended guidelines of 7 ppb. Of the contaminated wells 52 per cent contained adicarb between 8 and 30 ppb, 32 per cent between 31 and 75 ppb, and 16 per cent more that 75 ppb. Residents whose wells exceeded the guideline were advised not to use the water for drinking or cooking purposes and to obtain an alternate source of potable water. The Union Carbide Corporation provided those residents with activated carbon filtration units. The incident raises several serious issues, such as the testing of pesticides under field conditions prior to registration and during their use, the validity of the recommended actionable levels, and the paucity of long-term epidemiologic studies of the health effects resulting from consumption of pesticides in trace concentrations.

A progressive approach to the problem of foodborne infections

Qualitative and quantitative bacteriological examinations of 100 samples of perishable foods from 39 retail stores were performed to determine the presence of bacterial contaminants and to explore the feasibility of establishing and utilizing microbiological standards in enforcement. Forty-six per cent of the samples had standard plate counts in excess of 100,000 per gram, 17 per cent showed coliform organisms in excess of 100 per gram, 20 per cent revealed the presence of Staphylococcus aureus and 2 per cent Clostridium perfringens. None of the shell fish samples grew Vibrio parahaemolyticus. The bacteriological findings are discussed in relation to pertinent variables and the use of microbiological standards for potentially hazardous foods is explored. All 450 retail food establishments in a selected area of Western Suffolk County (New York) were subjected to comprehensive study, using a scoring system developed by the Food and Drug Administration. Initial inspections revealed 32 per cent as having one or more major violations. Follow-up inspections were performed to insure compliance and most violations were corrected within four weeks. Six months later all establishments were reinspected. The scoring system was found to have limited value. Half the establishments with major violations on initial inspection had major violations six months later as compared to less than a quarter of those with no initial major violation.