Reduced CTLA-4 signaling predisposes to Th2 driven gastric tumorigenesis

Anti-CTLA4 antibodies such as Yervoy, has been used in clinical practice to treat solid tumors. It supposed to work either by augmenting and revitalizing effector T cells function directly or indirectly through temporal silencing of inhibitory Foxp3+ Treg population or both. However, new study from Journal of Experimental Medicine showed that at least in [genetically predisposed] mice reduced CTLA-4 signaling by itself could cause Th2 driven tumorigenic transformation of stomach epithelial tissue.

For this study the authors created transgenic CTLA4 shRNA knockdown (CTLA4KD) mice on the BALB/c × C57BL/6 (B6) mixed genetic background. This they did because it appears that BALB/c but not B6 mice were susceptible developing gastric tumors in this model. CTLA4KD mice showed gastric epithelial transformation by 20w of age. Similarly, month long treatment of newborn BALB/c mice with anti-CTLA4 antibody also led to gastric epithelial transformation.

This tumorigenic transformation was CD4 T cell dependent and effector T cells from CTLA4KD but not from WT mice could mediate it. It indicated that changes in effector T cell composition and functionality were driving de novo inflammatory tumorigenesis.

Interestingly, gastric epithelial transformation were happening even in germ-free CTLA4KD mice lacking microbiota. However, since these mice also harbor increased numbers of inflammatory T cells, in all subsets analyzed such as Th1, Th2, Th17, and independent of microbiota it could indicate that T cells could be responding to antigens from food or environment.

Finally, elimination of canonical T helper cytokines showed that surprisingly neither IFN-γ nor IL-17 but IL-4 deficiency could abolish gastric epithelial transformation under conditions of reduced CTLA-4 activity.

In summary, this study suggests that inherited or clinically-induced reduction of CTLA-4 signaling in predisposed individuals could paradoxically lead to inflammatory tumorigenesis driven by type II immunity.

posted by David Usharauli

IL-33 → MyD88 pathway drives type II immunity in female genital mucosa

Type II immunity underlies several types of immune conditions such as asthma, allergy or response to parasitic helminths. It is not yet fully clear how type II immunity contributes to host's defenses. At this stage scientific inquiry is mostly focused on uncovering cellular and molecular mechanism behind type II immunity.

For example, PNAS has published new paper supporting role of locally produced IL-33 in promoting type II immunity.

For these experiments the authors have used papain, a well established experimental type II inducer protease. As reported before, papain required enzymatic activity for its type II response.

Papain application to female vaginal mucosa induced IL-33, a member of IL-1 family implicated in type II immunity.

Indeed, IL-33 deficient mice showed reduced secretion of components of type II immunity (IL-4, IgE).

Interestingly, type II immunity in response to papain in female genital tract depended on IRF4⁺ CD11c⁺ dendritic cells but it was independent of basophils and eosinophils.

Furthermore, type II immunity in response to papain application to female vaginal tissue depended on MyD88 signaling.  

In summary, this study confirms the role of IL-33 in type II immunity.

David Usharauli

Bifurcation of type 2 immunity

Type II immunity is referred to a Th2 dominant immune response to a wide array of proteases, venoms and mechanical irritants. Both innate ILC2 cells as well as adaptive Th2 cells are involved in this process. The relationship between innate and adaptive components of type II immunity is still being defined.

A new study from Richard Locksley's lab published in Nature Immunology showed that priming of Th2 cells in the lymph nodes and their subsequent type II effector functions in the peripheral tissues could be bifurcated.

For example, the authors showed that parasitic nematode Nippostrongylus brasiliensis (Nb)-infected mice triple deficient in sensing of TSLP, IL-25 and IL-33, the epithelial cytokines which have been linked to Th2 cell function, have normal lymph node IL-4+ Th2 differentiation and IgE production, but significantly diminished potential to secrete IL-13 and IL-5, effector Th2 cytokines, in the periphery. 

Importantly, such bifurcation of Th2 effector functionality was T cell intrinsic by sensing locally produced "release" cytokines, TSLP, IL-25 and IL-33.

In summary, this study indicate that even at the level of Th2 cells their effector functionality could be bifurcated depending on the local tissue micro-environment. This concept is important to better understand how to treat different types of allergies, for example, IL-4/IgE dominant systemic allergies versus IL-5/IL-13 dominant local tissue chronic allergies.     

David Usharauli

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

Is helminth infection sensed by latent virus?

During life time a human body is infected and re-infected with the same or the diverse types of infectious agents, sometimes simultaneously.

Since early 90's, an immune responses to infections were categorized into two major types: type 1, TH1 response, dominated by IFN-gamma (thought to be protective against viruses, intra-cellular pathogens, tumors) and type 2, TH2 response dominated by IL-4 (thought to to be protective against helminth infection). This division of labors, of course, is for simplicity purpose only.

Most importantly, since TH1 and TH2 responses thought to antagonize each other, it is clearly scientifically interesting to study and to know how immune system would deal with simultaneous presence of infections driving TH1 and TH2 responses.

The following Science paper has tried to answer this question. This study has examined the effect of an acute helminth infection on latent viral infection.

The authors has used a luciferase expression as a readout for latent viral reactivation. After initial viral infection and resting period (42 days), the mice were exposed to helminth or their eggs. Such exposure led to viral re-activation. 

 

It is of note, that very few peritoneal macrophages (< 0.02%) show sign of viral infection (RFP expression). Interestingly, the authors also observed that some of the virus infected macrophages expressed Arginase-1, a TH2 response signature molecule (though the numbers are so low that I am not sure whether it is real expression or an artifact). 

To understand the role of TH2 signature molecule, Arg1, in infected macrophages, the authors conducted the series of in vitro experiments with bone marrow derived macrophages infected with MHV86. These experiments showed that IL-4 and IL-13 (but not IL-5) were promoting viral infection of macrophages via STAT6 pathway.

This effect of IL-4 on MHV86 infection was antagonized by IFN-gamma.

Finally, in vivo experiments confirmed that IL-4 was promoting viral reactivation but only in absence of IFN-gamma signaling.

This effect was through STAT6. It should be noted here, however, that STAT6KO mice already showed high viral expression at day 0. This is unusual observation since IFN-gamma signaling should be more dominant in STAT6KO mice.

In summary, the authors proposed that in some situations, there is a competition between IL-4 and IFN-gamma responses on the level of viral promoters in infected cells.   

Few comments: First, a time has come to retire a simplified view of immune responses dominated either by IL-4 or IFN-gamma. Second, IL-4 was shown to not sufficient for viral reactivation. It requires inhibition of IFN-gamma signaling as well. No evidence is provided that helminth infection inhibits IFN-gamma signaling in latently infected macrophages. This study reminds me the story about in vitro TH17 induction that required the presence of anti-IFN-gamma and anti-IL-4 blocking antibodies to activate IL-17 program. Of course, this is a completely artificial system. Whether latent virus reactivation is IL-4 dependent in vivo is not clear either.

David Usharauli