IL-18 stimulates IL-13-mediated IFN-gamma-sensitive host resistance in vivo

Cathepsin L3 From Fasciola hepatica Induces NLRP3 Inflammasome Alternative Activation in Murine Dendritic Cells

The production of IL-1-family cytokines such as IL-1β and IL-18 is finely regulated by inflammasome activation after the recognition of pathogens associated molecular pattern (PAMPs) and danger associated molecular patterns (DAMPs). However, little is known about the helminth-derived molecules capable of activating the inflammasome. In the case of the helminth trematode Fasciola hepatica, the secretion of different cathepsin L cysteine peptidases (FhCL) is crucial for the parasite survival. Among these enzymes, cathepsin L3 (FhCL3) is expressed mainly in the juvenile or invasive stage. The ability of FhCL3 to digest collagen has demonstrated to be critical for intestinal tissue invasion during juvenile larvae migration. However, there is no information about the interaction of FhCL3 with the immune system. It has been shown here that FhCL3 induces a non-canonical inflammasome activation in dendritic cells (DCs), leading to IL-1β and IL-18 production without a previous microbial priming. Interestingly, this activation was depending on the cysteine protease activity of FhCL3 and the NLRP3 receptor, but independent of caspase activation. We also show that FhCL3 is internalized by DCs, promoting pro-IL-1β cleavage to its mature and biologically active form IL-1β, which is released to the extracellular environment. The FhCL3-induced NLRP3 inflammasome activation conditions DCs to promote a singular adaptive immune response, characterized by increased production of IFN-γ and IL-13. These data reveal an unexpected ability of FhCL3, a helminth-derived molecule, to activate the NLRP3 inflammasome, which is independent of the classical mechanism involving caspase activation.

Association of IL-13 rs20541 and rs1295686 variants with symptomatic asthma in a Saudi Arabian population

OBJECTIVE

Interleukin 13 (IL-13) plays a critical pro-inflammatory role in asthma. Several single nucleotide polymorphisms (SNPs) are associated with asthma susceptibility in specific populations; however, further replicative studies in other ethnic groups are mandatory.

METHODS

The association between IL-13 SNPs rs762534, rs20541, rs1295686, and rs1800925 (risk alleles A, A, T, and A, respectively) and asthma predisposition in a Saudi Arabian cohort was examined via a case-control cross-sectional study.

RESULTS

The frequencies of alleles between asthmatics and control populations were significantly different for rs20541 and rs1295686 SNPs (p < 0.001), whereas the frequencies of genotypes between asthmatics and controls were significantly different only for rs20541. The association of the risk (minor) alleles with asthma was examined using the dominant genetic model. Individuals with at least one copy of the risk alleles A (for rs20541) and T (for rs1295686) had significantly greater odds of being asthmatic (OR = 2.13, 95% CI = 1.39-3.26, p < 0.0001; OR = 1.69, 95% CI = 1.12-2.54, p = 0.008) relative to their most common homozygous genotypes. On the other hand, the minor A alleles for rs762534 and rs1800925 were not significantly associated with asthma risk. Regarding haplotype association analysis, individuals with at least one copy of the minor "risk" allele for both rs20541 and rs1295686 (CATG and CATA, respectively) had greater odds of being asthmatic relative to CGCG haplotype; however, this trend was not statistically significant (p > 0.3).

CONCLUSIONS

IL-13 minor T and A alleles for rs1295686 and rs20541, respectively, were associated with significantly higher risk of asthma in the Saudi Arabian population.

Homeostatic control of conjunctival mucosal goblet cells by NKT-derived IL-13

Although the effects of the interleukin 13 (IL-13) on goblet cell (GC) hyperplasia have been studied in the gut and respiratory tracts, its effect on regulating conjunctival GC has not been explored. The purpose of this study was to determine the major IL-13-producing cell type and the role of IL-13 in GC homeostasis in normal murine conjunctiva. Using isolating techniques, we identified natural killer (NK)/natural killer T (NKT) cells as the main producers of IL-13. We also observed that IL-13 knockout (KO) and signal transducer and activator of transcription 6 knockout (STAT6KO) mice had a lower number of periodic acid Schiff (PAS)+GCs. We observed that desiccating stress (DS) decreases NK population, GCs, and IL-13, whereas it increases interferon-γ (IFN-γ) mRNA in conjunctiva. Cyclosporine A treatment during DS maintained the number of NK/NKT cells in the conjunctiva, increased IL-13 mRNA in NK+ cells, and decreased IFN-γ and IL-17A mRNA transcripts in NK+ and NK- populations. C57BL/6 mice chronically depleted of NK/NKT cells, as well as NKT cell-deficient RAG1KO and CD1dKO mice, had fewer filled GCs than their wild-type counterparts. NK depletion in CD1dKO mice had no further effect on the number of PAS+ cells. Taken together, these findings indicate that NKT cells are major sources of IL-13 in the conjunctival mucosa that regulates GC homeostasis.

B cells have distinct roles in host protection against different nematode parasites

B cells can mediate protective responses against nematode parasites by supporting Th2 cell development and/or by producing Abs. To examine this, B cell-deficient mice were inoculated with Nippostrongylus brasiliensis or Heligmosomoides polygyrus. B cell-deficient and wild type mice showed similar elevations in Th2 cytokines and worm expulsion after N. brasiliensis inoculation. Worm expulsion was inhibited in H. polygyrus-inoculated B cell-deficient mice, although Th2 cytokine elevations in mucosal tissues were unaffected. Impaired larval migration and development was compromised as early as day 4 after H. polygyrus challenge, and administration of immune serum restored protective immunity in B cell-deficient mice, indicating a primary role for Ab. Immune serum even mediated protective effects when administered to naive mice prior to inoculation. This study suggests variability in the importance of B cells in mediating protection against intestinal nematode parasites, and it indicates an important role for Ab in resistance to tissue-dwelling parasites.

Disruption of Th2 immunity results in a gender-specific expansion of IL-13 producing accessory NK cells during helminth infection

Host gender has previously been identified as a determining factor in the resolution of Trichuris muris infection in mice lacking IL-4 (IL-4KO BALB/c). Worm expulsion in these mice is delayed, but occurs in females. In this study we were able to demonstrate delayed expulsion occurs at day 26 post infection and is associated with the production of the key Th2-associated cytokine IL-13 by both CD4(+) T cells and an auxiliary DX5(+) NK cell source, as well as a concurrent reduction in proinflammatory cytokines. NK cell number was comparably increased in both sexes, but NK cells from male mice were found to express higher levels of the chemokine receptor CXCR3. Depletion of CD4(+) T cells completely prevented parasite expulsion, whereas loss of NK cells resulted in a mild, but significant delay. Furthermore, IL-18 is a cytokine with the capacity to enhance both Th1 and Th2 responses found to be dispensable for worm expulsion in female mice but was a key factor for the suppression of the Th2 response in male IL-4KO mice. In contrast neutralization of IFN-gamma resulted in a complete restoration of typical wild-type BALB/c expulsion kinetics. This study sheds further light on the role of accessory NK cells in supplementing the IL-13-driven immune response when normal Th2 immunity is disrupted, and further identifies host gender as a key factor in determining the generation of "NK cell help".

The intestinal epithelium: sensors to effectors in nematode infection

The role of the intestinal epithelium as part of the physical barrier to infection is well established alongside its central roles in food absorption, sensing nutrients, and water balance. Nematodes are one of the most common types of pathogen to dwell in the intestine. This article reviews recent data that have identified crucial roles for intestinal epithelial cells in sensing these kinds of pathogens and initiating innate responses, which qualitatively influence adaptive immune responses against them. Moreover, it is now clear that the epithelium itself--in addition to the cells that lie within it--are key to many of the protective mechanisms that result in expulsion of these large multicellular parasites from the intestine. An understanding of the IEC and intraepithelial leukocyte response is crucial to both development of mucosal vaccines, and the mechanisms that underlie the emerging use of intestinal dwelling helminths for therapeutic treatments of inflammatory and autoimmune disease.

Promoter polymorphism of the IL-18 gene is associated with atopic asthma in Tunisian children

Several lines of evidence point to a relevant role of IL-18 in the process of asthma. Some studies suggest that the polymorphism in the gene of IL-18 can be involved in many inflammatory and atopic diseases such as asthma. The aim of our study is to estimate the frequency of the IL-18-607 C/A (rs 1946518) promoter polymorphism in Tunisian children with asthma. We investigated whether the presence of this polymorphism -607 C/A was associated with asthma or atopy and whether this polymorphism influenced the severity of asthma in affected children. We examined also the relationship between the IL-18 gene polymorphism and the serum total IgE level. The IL-18/-607 C/A polymorphism was analysed by polymerase chain reaction and restriction fragment-length polymorphism (PCR-RFLP) analysis. A total of 105 asthma patients and 112 controls as part of the whole children population were studied in a case-control study. Among the 105 children with asthma, 40 were also studied for linkage analyses with their respective parents. We noted that the A allele was associated with statistically significant increases in the risk of asthma in the case-control study (odd ratio (OR) = 1.55, 95% confidence interval (CI) 1.03-2.33. Moreover, the A allele was also associated with atopic asthma (P = 0.008), but not with asthma severity. The transmission disequilibrium test (TDT) analysis in this family study did not suggest a preferential transmission of the IL-18/ -607 C/A polymorphism to affected children. There is no correlation between the IgE level and the IL-18 -607 C/A promoter polymorphism. Our data indicate that IL-18 -607 C/A promoter polymorphism is associated with susceptibility to developing asthma in Tunisian population.