Type I IFN-mediated regulation of IL-1 production in inflammatory disorders

Although contributing to inflammatory responses and to the development of certain autoimmune pathologies, type I interferons (IFNs) are used for the treatment of viral, malignant, and even inflammatory diseases. Interleukin-1 (IL-1) is a strongly pyrogenic cytokine and its importance in the development of several inflammatory diseases is clearly established. While the therapeutic use of IL-1 blocking agents is particularly successful in the treatment of innate-driven inflammatory disorders, IFN treatment has mostly been appreciated in the management of multiple sclerosis. Interestingly, type I IFNs exert multifaceted immunomodulatory effects, including the reduction of IL-1 production, an outcome that could contribute to its efficacy in the treatment of inflammatory diseases. In this review, we summarize the current knowledge on IL-1 and IFN effects in different inflammatory disorders, the influence of IFNs on IL-1 production, and discuss possible therapeutic avenues based on these observation

Innate and adaptive effects of inflammasomes on T cell responses

Inflammasomes are protein complexes that form in response to pathogen-derived or host-derived stress signals. Their activation leads to the production of inflammatory cytokines and promotes a pyrogenic cell death process. The massive release of inflammatory mediators that follows inflammasome activation is a key event in alarming innate immune cells. Growing evidence also highlights the role of inflammasome-dependent cytokines in shaping the adaptive immune response, as exemplified by the capacity of IL-1β to support Th17 responses, or by the finding that IL-18 evokes antigen-independent IFN-γ secretion by memory CD8+ T cells. A deeper understanding of these mechanisms and on how to manipulate this powerful inflammatory system therefore represents an important step forward in the development of improved vaccine strategies. © 2013 Elsevier Ltd

Human Papillomavirus Deregulates the Response of a Cellular Network Comprising of Chemotactic and Proinflammatory Genes

Despite the presence of intracellular pathogen recognition receptors that allow infected cells to attract the immune system, undifferentiated keratinocytes (KCs) are the main targets for latent infection with high-risk human papilloma viruses (hrHPVs). HPV infections are transient but on average last for more than one year suggesting that HPV has developed means to evade host immunity. To understand how HPV persists, we studied the innate immune response of undifferentiated human KCs harboring episomal copies of HPV16 and 18 by genome-wide expression profiling. Our data showed that the expression of the different virus-sensing receptors was not affected by the presence of HPV. Poly(I:C) stimulation of the viral RNA receptors TLR3, PKR, MDA5 and RIG-I, the latter of which indirectly senses viral DNA through non-self RNA polymerase III transcripts, showed dampening in downstream signalling of these receptors by HPVs. Many of the genes downregulated in HPV-positive KCs involved components of the antigen presenting pathway, the inflammasome, the production of antivirals, pro-inflammatory and chemotactic cytokines, and components downstream of activated pathogen receptors. Notably, gene and/or protein interaction analysis revealed the downregulation of a network of genes that was strongly interconnected by IL-1β, a crucial cytokine to activate adaptive immunity. In summary, our comprehensive expression profiling approach revealed that HPV16 and 18 coordinate a broad deregulation of the keratinocyte's inflammatory response, and contributes to the understanding of virus persistence

The Nlrp3 inflammasome regulates acute graft-versus-host disease

The success of allogeneic hematopoietic cell transplantation is limited by acute graft-versus-host disease (GvHD), a severe complication accompanied by high mortality rates. Yet, the molecular mechanisms initiating this disease remain poorly defined. In this study, we show that, after conditioning therapy, intestinal commensal bacteria and the damage-associated molecular pattern uric acid contribute to Nlrp3 inflammasome-mediated IL-1β production and that gastrointestinal decontamination and uric acid depletion reduced GvHD severity. Early blockade of IL-1β or genetic deficiency of the IL-1 receptor in dendritic cells (DCs) and T cells improved survival. The Nlrp3 inflammasome components Nlrp3 and Asc, which are required for pro-IL-1β cleavage, were critical for the full manifestation of GvHD. In transplanted mice, IL-1β originated from multiple intestinal cell compartments and exerted its effects on DCs and T cells, the latter being preferentially skewed toward Th17. Compatible with these mouse data, increased levels of active caspase-1 and IL-1β were found in circulating leukocytes and intestinal GvHD lesions of patients. Thus, the identification of a crucial role for the Nlrp3 inflammasome sheds new light on the pathogenesis of GvHD and opens a potential new avenue for the targeted therapy of this severe complication

NLRC5 Exclusively Transactivates MHC Class I and Related Genes through a Distinctive SXY Module

MHC class II (MHCII) genes are transactivated by the NOD-like receptor (NLR) family member CIITA, which is recruited to SXY enhancers of MHCII promoters via a DNA-binding "enhanceosome" complex. NLRC5, another NLR protein, was recently found to control transcription of MHC class I (MHCI) genes. However, detailed understanding of NLRC5's target gene specificity and mechanism of action remained lacking. We performed ChIP-sequencing experiments to gain comprehensive information on NLRC5-regulated genes. In addition to classical MHCI genes, we exclusively identified novel targets encoding non-classical MHCI molecules having important functions in immunity and tolerance. ChIP-sequencing performed with Rfx5(-/-) cells, which lack the pivotal enhanceosome factor RFX5, demonstrated its strict requirement for NLRC5 recruitment. Accordingly, Rfx5-knockout mice phenocopy Nlrc5 deficiency with respect to defective MHCI expression. Analysis of B cell lines lacking RFX5, RFXAP, or RFXANK further corroborated the importance of the enhanceosome for MHCI expression. Although recruited by common DNA-binding factors, CIITA and NLRC5 exhibit non-redundant functions, shown here using double-deficient Nlrc5(-/-)CIIta(-/-) mice. These paradoxical findings were resolved by using a "de novo" motif-discovery approach showing that the SXY consensus sequence occupied by NLRC5 in vivo diverges significantly from that occupied by CIITA. These sequence differences were sufficient to determine preferential occupation and transactivation by NLRC5 or CIITA, respectively, and the S box was found to be the essential feature conferring NLRC5 specificity. These results broaden our knowledge on the transcriptional activities of NLRC5 and CIITA, revealing their dependence on shared enhanceosome factors but their recruitment to distinct enhancer motifs in vivo. Furthermore, we demonstrated selectivity of NLRC5 for genes encoding MHCI or related proteins, rendering it an attractive target for therapeutic intervention. NLRC5 and CIITA thus emerge as paradigms for a novel class of transcriptional regulators dedicated for transactivating extremely few, phylogenetically related genes

NLRC5 selectively occupies MHCI gene promoters.

<p>(A) NLRC5-ChIPseq tracks are shown for the CIITA targets <i>H2-DMb1</i>, <i>H2-Aa</i> and <i>IncRNA/H2-Eb1</i>. The tracks depict reads mapping to regions spanning between 5kb upstream and 5kb downstream of the TSS. After normalization as rpm (reads per million), read coverage was expressed relative to the average value observed for all NLRC5-binding peaks. TSSs are positioned as annotated in ENSEMBL. (B) Antibodies specific for NLRC5 and CIITA were used to immunoprecipitate cross-linked chromatin fragments derived from <i>Nlrc5</i>^<i>+/-</i><i>CIIta</i>^<i>+/-</i>, <i>Nlrc5</i>^{<i>−/−</i>}, <i>CIIta</i>^{<i>−/−</i>}, and <i>Nlrc5</i>^{<i>−/−</i>}<i>CIIta</i>^{<i>−/−</i>} B cells. Immunoprecipitates were analyzed by quantitative PCR for the abundance of promoter sequences from the indicated genes. Relative promoter binding is shown. The average ± SEM of three experiments are depicted. Statistical significance was calculated using an unpaired Student’s <i>t</i>-test. (C) A phylogenetic tree is shown for classical and non-classical MHCI and MHCII genes. Genes regulated by NLRC5 and those regulated by CIITA are indicated in blue and green font, respectively. Clusters of classical, young and middle-aged MHCI genes are highlighted.</p

NLRC5 and CIITA exhibit non-redundant functions.

<p>(A and B) MHCI and MHCII expression were assessed in the indicated splenic cells from <i>Nlrc5</i>^<i>+/−</i><i>CIIta</i>^<i>+/−</i>, <i>Nlrc5</i>^{<i>−/−</i>}, <i>CIIta</i>^{<i>−/−</i>}, and <i>Nlrc5</i>^{<i>−/−</i>}<i>CIIta</i>^{<i>−/−</i>} mice. Histogram overlays show H2-K or MHCII expression for control (dashed line), <i>Nlrc5</i>^−/− (filled dark grey), <i>CIIta</i>^−/− (filled light grey), and double-deficient (solid line) mice. Graphs depict the MFIs of H2-K for CD8⁺ T cells (gated as CD3⁺CD8⁺), CD4⁺ T cells (gated as CD3⁺CD4⁺), NK cells (gated as NK1.1⁺CD3^-), and NKT cells (gated as NK1.1⁺CD3⁺) (A), or B cells (gated as CD19⁺) and DCs (gated as CD11c^hiCD11b^int-hi) (B) in control (n = 9), <i>Nlrc5</i>^−/− (n = 10), <i>CIIta</i>^−/− (n = 9), and double-deficient (n = 8) mice (A and B). For B cells and DCs, graphs also show the MFI of MHCII. MFIs of control mice were set at 100%. (A and B) Results depict the mean ± SEM from three pooled experiments. Statistical significance of the differences between multiple groups was analyzed by 2-way ANOVA adjusted by Bonferroni correction over 6 (H2-K) or 2 (MHCII) samples, and is indicated only for differences between single and double-deficient groups (i.e., the interaction between the two groups).</p

NLRC5 deficiency selectively impairs MHC class idependent lymphocyte killing by cytotoxic T cells

Nucleotide-binding oligomerization domain-like receptors (NLRs) are intracellular proteins involved in innate-driven inflammatory responses. The function of the family member NLR caspase recruitment domain containing protein 5 (NLRC5) remains a matter of debate, particularly with respect to NF-kappa B activation, type I IFN, and MHC I expression. To address the role of NLRC5, we generated Nlrc5-deficient mice (Nlrc5(Delta/Delta)). In this article we show that these animals exhibit slightly decreased CD8(+) T cell percentages, a phenotype compatible with deregulated MHC I expression. Of interest, NLRC5 ablation only mildly affected MHC I expression on APCs and, accordingly, Nlrc5(Delta/Delta) macrophages efficiently primed CD8(+) T cells. In contrast, NLRC5 deficiency dramatically impaired basal expression of MHC I in T, NKT, and NK lymphocytes. NLRC5 was sufficient to induce MHC I expression in a human lymphoid cell line, requiring both caspase recruitment and LRR domains. Moreover, endogenous NLRC5 localized to the nucleus and occupied the proximal promoter region of H-2 genes. Consistent with downregulated MHC I expression, the elimination of Nlrc5(Delta/Delta) lymphocytes by cytotoxic T cells was markedly reduced and, in addition, we observed low NLRC5 expression in several murine and human lymphoid-derived tumor cell lines. Hence, loss of NLRC5 expression represents an advantage for evading CD8(+) T cell-mediated elimination by downmodulation of MHC I levels-a mechanism that may be exploited by transformed cells. Our data show that NLRC5 acts as a key transcriptional regulator of MHC I in lymphocytes and support an essential role for NLRs in directing not only innate but also adaptive immune responses. The Journal of Immunology, 2012, 188: 3820-3828

The S box sequence is required for NLRC5-mediated transactivation.

<p>(A) Alignment of SXY regions of <i>H2-K</i> and <i>H2-Eb (H2-E)</i>. Bold letters indicate the most conserved sequences in the S, X, and Y motifs; boxes define the regions that were used to generate hybrid promoters 1–6 (see <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1005088#sec010" target="_blank">Material and Methods</a>) shown in C. (B) Luciferase reporter gene analyses were performed in HEK293T cells co-transfected with the <i>H2-K</i> or <i>H2-Eb</i> reporter constructs and either empty vector (e.v.) or expression vectors encoding NLRC5 or CIITA. Data represent mean ± SD of technical triplicates expressed as fold induction over e.v. and are representative of at least three experiments. Statistical significance was calculated using an unpaired Student’s <i>t</i>-test, two-tailed. (C) Luciferase reporter gene analyses were performed in HEK293T cells co-transfected with empty or NLRC5-encoding expression vectors and the WT (<i>H2-K</i>, <i>H2-E</i>) or hybrid (H2-K/E 1–6) promoter constructs depicted schematically below: <i>H2-K</i> and <i>H2-Eb</i> derived sequences are represented by blue and green, respectively. Data are expressed as fold induction over e.v. and represent mean ± SEM of four independent experiments. Statistical significance was calculated using an unpaired Student’s <i>t</i>-test, two-tailed.</p