Inflammation modifies pattern of differentiation of commensal-specific T cells

1. #Commnesal S. epidermidis–specific -#MIIINA:H2-M3+ CD8+ T cells ordinarily differentiate into Tc1 or Tc17 subsets. However, when co-exposed to chitin or sand fly (source of #inflammation), Tc17 subset also produce type II cytokines. pic.twitter.com/g9Wy7BncPD

— David Usharauli (@3DiMMUNE) January 10, 2019

3. In any case, such deviation into type II cytokine+ lineage during co-exposure to S. epidermidis and inflammation is specific for CD8+CCR6+ cells (referred to as Tc17). pic.twitter.com/6uNCVHMtEz

— David Usharauli (@3DiMMUNE) January 10, 2019

5. The authors tried to show how skin #Treg deficiency could have the same effect on Tc17 de-differentiation. Again. the authors failed to show that IL-17+ and IL-5/IL-13+ Tc17 cells overlap. They don't. They put in suppl material these #data. Should be in main paper. pic.twitter.com/QupGc7HWLo

— David Usharauli (@3DiMMUNE) January 10, 2019

7. But again, no evidence is provided that IL-17+ T cells co-express IL-5 or IL-13 when exposed to IL-18. Exactly opposite. No overlap. pic.twitter.com/QG8U9EBSSH

— David Usharauli (@3DiMMUNE) January 10, 2019

So, what is my conclusions: this paper does not support the authors' conclusions about Tc17 acquiring Tc2 phenotype. Yes, it is true that RORgt+ or CCR6+ CD8+ T cells could acquire Tc2 phenotype but the same not true IL-17+ Tc17 cells or at least data are not there.

— David Usharauli (@3DiMMUNE) January 10, 2019

IL-4R mutation drives IL-17 dominant asthma phenotype

Asthma represents a dysregulated immune response to antigens that normally do not produce clinically-detectable immune responses. Ordinarily asthma response was regarded as classical Th2 class response with dominant IL-4/IL-13/eosinophil axis. However, for past 10 years, since the discovery of Th17 cells, scientists started to find a separate subtype of asthma dominated by IL-17/neutrophil axis. 

New paper in Nature Medicine pinpointed one molecular mechanism that underlie Th2→Th17 switch in asthma. It showed that a single amino acid mutation in IL-4Rα introduces instability in regulatory T cell lineage leading to Th17 induction.

Initially, the authors observed that mice with a glutamine (Q)-to-arginine (R) substitution at amino acid residue 576 of IL-4Rα (Il4ra^R576 mice) develop more severe experimental asthma in response house dust mite allergen.

In vitro culture of conventional or induced regulatory T cells derived from mice on Il4ra^R576 background showed exaggerated IL-17 expression in response to TGFβ1 and IL-4.

Lineage tracing analysis revealed instability of regulatory T cell lineage and their differentiation into IL-17 producing cells (ex-Tregs).

Indeed, when Tregs were rendered incapable to differentiate into IL-17 producing cells in Foxp3^YFPCreRorc^Δ/Δ mice, severity of asthma was reduced.

In summary, this study showed that genetic mutation in IL-4Rα introduces instability in Treg lineage and leads to IL-17 dominant asthma phenotype. Such asthma conversion is expected to be sensitive to anti-IL6 therapy.

David Usharauli

Gut-specific eosinophils suppress IL-17 production by antagonizing IL-1 signaling

Prior to discovery of Toll-like receptors (TLR) in late 90s, immunology was dominated by concepts involving adaptive immune cells. However, for past 15 years it has become evident that innate immune cells of "all shapes and forms that exist out there" are equal partners with T and B cells and frequently provide instructions and actually control the magnitude and directions of adaptive immune response. For example, development of successful, next generation vaccines would require incorporation of these new concepts. 

It seems innate immune system is even more complex and unpredictable than T or B cells are. For instance, this week Journal of Experimental Medicine published new study wherein the authors reported that eosinophils, a cell population usually implicated in allergy and anti-helminth response, suppressed Th17 cells by antagonizing IL-1 signaling.

First, the authors observed that Th17 cells in ΔdblGATA-1 mice [which lack eosinophil-lineage cells] were significantly increased in the small intestine, but not in the spleen or mesenteric LNs (MLNs).

In vitro generation of Th17 cells were inhibited by presence of small intestinal eosinophils. 

Functional profiling revealed that small intestinal eosinophils secreted high amount of IL-1 receptor antagonist (IL-1Ra), which competes with IL-1β for receptor binding (IL-1 signaling is involved in Th17 development).

Interestingly, eosinophils were the major producers of IL-1Ra in small intestine, since no IL-1Ra was detected in small intestinal tissue from ΔdblGATA-1 mice. Of note, eosinophils from blood or bone marrow produced little or no IL-1Ra. 

In addition, the authors showed that small intestinal eosinophils derived from MyD88-KO or Germ Free (GF) mice produced WT-level IL-1Ra, suggesting its independence from gut flora or major TLR signaling.

Role of IL-1Ra in eosinophil mediated Th17 suppression in small intestine was confirmed in experiments with eosinophils derived from IL-1Ra-KO mice.   

In summary, this study showed that small intestine harbors specialized eosinophils secreting high amount of IL-1Ra and suppressing steady-state development of Th17. 

David Usharauli

Gut microbiota, not IL-17, is required for spontaneous arthritis in K/BxN mice

IL-17 has been implicated in autoimmune inflammatory diseases such as arthritis. It was proposed that gut microbiota, [SFB]-induced Th17 cells were mediating autoimmune arthritis. Experiments with K/BxN mouse, a human model of spontaneous autoimmune [rheumatoid] arthritis, provided the initial support for this hypothesis. 

However, a new paper in Journal of Immunology, suggests that IL-17 may have nothing to do with arthritis in K/BxN mice.

For this study, the authors have generated K/BxN mice deficient for IL-17A. Surprisingly, IL-17 deficient K/BxN mice showed no difference in arthritis development compared to WT K/BxN mice.

Even though IL-17 deficient K/BxN mice had no Th17 cells, levels of anti-GPI IgG auto-antibodies were not affected by absence of IL-17. 

Next, the authors showed that antibiotic treatment could inhibit arthritis development in K/BxN mice independent of IL-17 expression.  

Interestingly, the authors found that K/BxN mice with CD4-specific deletion of Bcl6 [and lacking T follicular helper T cells, Tfh] were resistant for arthritis development, implying role of Tfh and auto-antibodies in arthritis pathology [independent of IL-17].

In summary, this study suggests that IL-17 may not be involved in development of autoimmune [rheumatoid] arthritis in all cases. Rather, it is gut microbiota and Tfh/Ab that play dominant "pathogenic" role in this autoimmune disease.

David Usharauli

α-IL23, not α-IL17 antibody blockade, shows protection in IBD model

Previous studies indicated that cytokines IL-23 and IL-17 act in concert to induce and perpetuate autoimmune inflammation. This is certainly true for psoriatic skin inflammation.

However, two new back-to-back studies in journal Immunity provided evidence that when it comes to intestine inflammation, role of IL-23 and IL-17 goes in opposite direction. Here, blockade of IL-17 exacerbate while blockade of IL-23 inhibits intestine pathology and gut wall permeability.

Both studies came from research groups working in biotech/biopharma (Daniel Cua's group at Merck Research Laboratories and Jennifer Towne's group at Amgen [presently at Janssen]). Both studies reached similar conclusions. 

Here, the authors treated colitis-prone mice with blocking antibodies specific for IL-23 or IL-17 cytokine family. Surprisingly, both α-IL17A or α-IL17RA treatment worsened gut pathology, while α-IL23 (p40 or p19 subunits) antibody showed protection.

Unlike α-IL23, α-IL17RA antibody treatment was associated with increased gut wall permeability (serum sCD14 and LBP), implying IL-17 role in gut health.

Similar increased gut leakage (with FITC-dextran) was observed by Merck's team in chemical irritant DSS-induced GI inflammation model in IL-17KO mice (though Amgen's team did not observe it in DSS mouse model with α-IL17 treatment. It could be that α-IL17 antibody blockade did not fully inhibit IL-17 action as it could be expected in IL-17KO mice).

Additional experiments showed that γδ T cells were the main producers of gut IL-17 in DSS model and that γδ T cell KO mice showed the same increased GI tract permeability as IL-17KO mice.

Finally, Merck's team showed that (a) γδ T cell-derived IL-17 production in the gut were mostly IL-23 independent and (b) IL-23rKO mice were protected against worsening GI wall pathology.

In overall, these two studies suggest that local gut tissue associated IL-23 independent but γδ T cell-derived IL-17 production plays a protective role in gut permeability. Basically, this means that α-IL23 blockade, but not α-IL17 pathway inhibition, would most likely provide benefits to patients suffering from GI tract idiopathic inflammation.

David Usharauli

Species-specific microbial attachment to host epithelial cells determines gut IL-17 induction

Gut microbes drive maturation of host's immune system. Not every microbe is able to do it, however. So what microbial qualities determines its impact on host?  

New paper in journal Cell has revealed a simple rule of thumb: microbes that could attach themselves to gut epithelial cells drove induction of local Th17 cells and IgA. Interestingly this microbial quality found to be species-specific. 

Initially, the authors showed that monocolonization of germ-free mice or rats with endogenous segmented filamentous bacteria  (mouse-SFB and rat-SFB) induced Th17 cells in a species-specific manner (mouse data are shown here ).   

Ex vivo stimulation of lamina propria cells with autoclaved fecal antigens (A/C) showed that IL-17 secretion and IgA production were correlated with species-specific access to SFB antigens in the gut.

Additional experiments with WT microbes or microbes lacking adhesion molecules confirmed that epithelial adhesion determined IL-17/IgA production.

In summary, these results indicate that direct adhesion to gut epithelial cells is necessary pre-condition for local immune response induction. Mechanistically, this adhesion by microbes induces production of serum amyloid A (SAA) that primed local T cells for Th17 phenotype.

David Usharauli

  

Pain sensing neurons alert dendritic cells for presence of skin fungal parasites

IL-23/IL-17 axis plays important role in the host's defense against fungal parasites. Recent studies show that skin CD11b⁺ dendritic cells and skin γδ T cells contribute for anti-fungal protection.

New study in journal Immunity added yet another layer of protection to the skin. It showed that skin pain and thermal sensing TRPV1 neurons also sensing the presence of fungal parasite and alert local immune defense system.

Using mouse model of candida albicans fungal infection, the authors first re-confirmed that cytokine IL-17 showed anti-fungal activity.

Next, the authors showed that the source of this protective IL-17 were skin γδ T cells (and not conventional αβ T cells or non-conventional dendritic epidermal T cells (DETCs).

Next, the authors re-confirmed that IL-23 was upstream of IL-17 in host's protection against candida albicans fungal infection.

Next, the authors showed that skin langerhans cells (LCs) and Batf3 ⁺ CD103⁺ DCs (LC^Δ Batf3 ^Δ) were dispensable for anti-fungal protection.

However, the authors found that IL-23 derived from C-type lectin positive dermal DCs (using Mgl2-DTR + IL-23KO BM chimera) were necessary for this protection.

Afterwards, the authors found that ablation of skin nociceptors, TRPV1, decreased anti-fungal protection.

Finally, the authors found that upon detection of candida albicans, CGRP (calcitonin gene related peptide) secreted by TRPV1 neurons acted on Mgl2+ dermal DCs to induce IL-23 secretion that in turn induce protective IL-17 from local skin γδ T cells (strangely, however, Fig. 6H and 6I do not match the authors text in the results. Here, -DT+CGRPα samples should have significantly lower CFU compared to +DT+CGRPα samples, since DT depletes Mgl2+ DCs).

In summary, these results provide additional support for neuro-immune network affecting host's protection against infection. This does not mean that neurons are important for ultimate clearance of the pathogen. Here, the authors only showed day 3 of infection when there is a maximum burden of fungal pathogen.

However, there is also a broader implications. Mainly, how CNS can influence or even imitate local immune response and produce or augment skin inflammation such as in psoriasis, dermatitis, eczema, urticaria and skin allergies.  

David Usharauli

Tumor converts neutrophils into metastasis-promoting cells via γδ T cell-derived IL-17

Immune system supposed to defend the body from infectious agents and genetically transformed cells (tumors). Usually, at the end of each immune response, that can be quite damaging (immune phase), immune cells will be involved in tissue healing, regeneration or remodeling (adaptation phase). However, sometimes infectious agents or tumors will circumvent these steps and jump directly to adaptation phase and will recruit immune cells to carry out their "agenda" at the expense of the host.

For example, we can speculate that tumor's "agenda" would be to grow and expand (metastasize). However, neither of these possible without local and distant tissue remodeling and its readiness to accommodate (accept) tumor cells. Here is where local immune cells become involved.

New study in journal Nature points to one of those possibilities. The authors showed that in a mouse model of mammary tumor metastasis, neutrophils promotes tumor lung metastasis via IL-17 produced by circulating γδ-T cells.

I would like to point out that the authors have used tumor transplantation model (to have shorter experiments) that is obviously very different from spontaneously arising tumors. Nevertheless, they found that lung or lymph node metastasis of skin transplanted tumor was reduced with neutrophil depletion using α-Ly6G antibody (this antibody supposedly selectively depletes neutrophils since they express it at high level).

Interestingly, tumor metastasis were also reduced in the recipients devoid of adaptive immune system and correlated with reduction of IL-17 and G-CSF (granulocyte colony-stimulating factor) serum levels.

Finally, the authors showed that γδ-T cell depletion or genetic deficiency reduced lung and lymph node metastasis of transplanted tumor.

In summary, these results suggest that tumor cells exploit not yet identified pathways within immune system (γδ-T cells / IL-17 / neutrophils axis) to prepare distant tissues to accommodate tumor colonies coming from original tumor niche. Only by understanding how immune cells interact with normal tissues during or after immune response, could we design ways to block such metastasis.

In general this paper is OK, especially if one considers other papers (two recent papers in JEM) corroborating the idea of IL-17's involvement in tumor initiation and metastasis. However, some data are not clear or not well explained, so not a Nature caliber paper, in my view. For example, in Fig. 3a, treatment with α-IL-17A did not modify IL-17 level in the serum. Also, the authors did not explain why they thought CD8 T cells were protective against metastasis in this model when tumor-bearing RAG KO hosts, which lack CD8 T cells, did not show increased metastasis (Fig. 2d versus. Fig. 3g)?


David Usharauli