Blocking of mast cell-mediated passive anaphylaxis to peanut using covalent heterobivalent inhibitor in a humanized mouse model

Anaphylaxis to peanut allergen is a severe hypersensitive allergic reaction characterized by life-threatening symptoms. Anaphylaxis is mediated by IgE-dependent mast cell activation that leads to the release of inflammatory mediators. In a previous report, we described the design of a covalent heterobivalent inhibitor (cHBI) that selectively forms covalent bonds with allergen specific-IgE (sIgE) on mast cells and abates allergic reactions in ex-vivo peanut challenges. Here, we utilized a humanized mouse model to recapitulate key features of anaphylaxis to peanut in humans, and we examined the efficacy of cHBI in blocking the anaphylactic reaction in this model. NSGS (NOD-scid Il2rgnull IL-3/GM-CSF/SCF) mice engrafted with human hematopoietic stem cells were treated with an allergen-specific human IgE monoclonal antibody and then challenged with a peanut allergen. We found that the peanut-challenged humanized mice can develop rapid anaphylaxis and mast cell degranulation following challenge. The anaphylactic reaction was characterized by a substantial decline of core body temperatures and upregulation of human mast cell degranulation markers. Additionally, we found that the severity of the anaphylactic reaction is hIgE dose-dependent. Most importantly, cHBI protected the mice from developing an anaphylactic reaction demonstrating the ability of cHBI to block IgE-mediated allergic reactions in the humanized mice. Overall, our results show that the humanized mouse model is a novel model to study human mast cell IgE-mediated allergic reactions and demonstrate that cHBI is an effective potential therapeutic inhibitor for food allergy.

A single cell approach to identify the role of IL-9 secreting tissue-resident CD4+ T cells in allergic airway recall responses

Allergic asthma is a chronic intermittent inflammatory lung disease where patients experience relatively few symptoms between exacerbations precipitated by allergen-challenge of allergic memory responses. Allergen-specific CD4+ T cells are believed to be a major mediator of allergic memory responses through the production of type 2 cytokines including IL-4, IL-5, IL-13 and IL-9. Recently, tissue-resident memory (Trm) cells have been identified in peripheral tissues that mediate mucosal barrier immunity. However, the precise role of Trm CD4+ T cells in allergic exacerbations is not clearly defined. In studies to examine the role of IL-9 in allergen-specific Trm responses to Aspergillus fumigatus we observed that all IL-9-secreting T cells had a resident memory phenotype. Inhibition of circulating T cells by administering FTY720 in the last month of rest, diminished the total CD4 T cells population in the lung, while the Th9 cells remained stable. Blockade of IL-9 prior to recall challenge phase reduced overall allergic lung inflammation as assessed both by flow cytometry and single cell RNA-seq. Within eight hours after challenge, IL-9 is one of the top genes identified by scRNA-seq that distinguishes ST2+ and ST2− CD4+ T cell populations in the lung. Using IL-9-reporter mice we also compared gene expression in isolated IL-9+ T cells and other type 2 T cells. These findings demonstrate that IL-9-producing Trms play an important role in mediating allergic memory responses. IL-9 could be a promising therapeutic target specifically in patients showing symptoms of intermittent allergic response.

Blimp1 Prevents Methylation of Foxp3 and Loss of Regulatory T Cell Identity at Sites of Inflammation

Foxp3⁺ regulatory T (Treg) cells restrict immune pathology in inflamed tissues; however, an inflammatory environment presents a threat to Treg cell identity and function. Here, we establish a transcriptional signature of central nervous system (CNS) Treg cells that accumulate during experimental autoimmune encephalitis (EAE) and identify a pathway that maintains Treg cell function and identity during severe inflammation. This pathway is dependent on the transcriptional regulator Blimp1, which prevents downregulation of Foxp3 expression and “toxic” gain-of-function of Treg cells in the inflamed CNS. Blimp1 negatively regulates IL-6- and STAT3-dependent Dnmt3a expression and function restraining methylation of Treg cell-specific conserved non-coding sequence 2 (CNS2) in the Foxp3 locus. Consequently, CNS2 is heavily methylated when Blimp1 is ablated, leading to a loss of Foxp3 expression and severe disease. These findings identify a Blimp1-dependent pathway that preserves Treg cell stability in inflamed non-lymphoid tissues.

•

Most Foxp3⁺ Treg cells in the inflamed CNS express Blimp1

•

Blimp1 inhibits Dnmt3a and prevents methylation of the Foxp3 locus

•

IL-6 contributes to methylation of the Foxp3 locus in a Dnmt3a-dependent manner

•

Blimp1 counteracts the IL-6-driven destabilization of Treg cells

Is the HERV-K HML-2 Xq21.33, an endogenous retrovirus mutated by gene conversion of chromosome X in a subset of African populations, associated with human breast cancer?

The human endogenous retroviruses HERV-K HML-2 have been considered a possible cause of human breast cancer (BrC). A HERV-K HML-2 fully intact provirus Xq21.33 was recently identified in some West African people. We used PCR technology to search for the Xq21.33 provirus in DNA from Nigerian women with BrC and controls. to see if Xq21.33 plays any role in predisposing to BrC. This provirus was detected in 27 of 216 (12.5%) women with BrC and in 22 of 219 (10.0%) controls. These results were not statistically significant. The prevalence of provirus in premenopausal control women 44 years or younger [18/157 (11.46%)} vs women with BrC [12/117 (10.26%)] showed no statistical difference. The prevalence of virus in postmenopausal control women > 45 yrs. was 7.4% (4/54) vs 15.31% (15/98) in postmenopausal women with BrC. These changes were not statistically significant at <.05, but the actual p value of <.0.079, suggests that Xq21.33 might play some role in predisposing to BrC in postmenopausal women. Provirus was present in Ghanaian women (6/87), in 1/6 Pygmy populations and in African American men (4/45) and women (6/68), but not in any Caucasian women (0/109). Two BrC cell lines (HCC 70 and DT22) from African American women had Xq21.33. Env regions of the virus which differed by 2-3 SNPs did not alter the protein sequence of the virus. SNP at 5730 and 8529 were seen in all persons with provirus, while 54% had an additional SNP at 7596.Two Nigerian women and 2 Ghanaian women had additional unusual SNPs. Homozygosity was seen in (5/27) BrC and (2/22) control women. The genetic variation and homozygosity patterns suggested that there was gene conversion of this X chromosome associated virus. The suggestive finding in this preliminary data of possible increased prevalence of Xq21.33 provirus in post-menopausal Nigerian women with BrC should be clarified by a more statistically powered study sample to see if postmenopausal African and/or African American women carriers of Xq21.33 might show increased risk of BrC. The implication of finding such a link would be the development of antiretroviral drugs that might aid in preventing BrC in Xq21.33+ women.

Calcitriol Regulates the Differentiation of IL-9-Secreting Th9 Cells by Modulating the Transcription Factor PU.1

Vitamin D can modulate the innate and adaptive immune system. Vitamin D deficiency has been associated with various autoimmune diseases. Th9 cells are implicated in the pathogenesis of numerous autoimmune diseases. Thus, we investigated the role of calcitriol (active metabolite of vitamin D) in the regulation of Th9 cell differentiation. In this study, we have unraveled the molecular mechanisms of calcitriol-mediated regulation of Th9 cell differentiation. Calcitriol significantly diminished IL-9 secretion from murine Th9 cells associated with downregulated expression of the Th9-associated transcription factor, PU.1. Ectopic expression of VDR in Th9 cells attenuated the percentage of IL-9-secreting cells. VDR associated with PU.1 in Th9 cells. Using a series of mutations, we were able to dissect the VDR domain involved in the regulation of the Il9 gene. The VDR-PU.1 interaction prevented the accessibility of PU.1 to the Il9 gene promoter, thereby restricting its expression. However, the expression of Foxp3, regulatory T cell-specific transcription factor, was enhanced in the presence of calcitriol in Th9 cells. When Th9 cells are treated with both calcitriol and trichostatin A (histone deacetylase inhibitor), the level of IL-9 reached to the level of wild-type untreated Th9 cells. Calcitriol attenuated specific histone acetylation at the Il9 gene. In contrast, calcitriol enhanced the recruitment of the histone modifier HDAC1 at the Il9 gene promoter. In summary, we have identified that calcitriol blocked the access of PU.1 to the Il9 gene by reducing its expression and associating with it as well as regulated the chromatin of the Il9 gene to regulate expression.

Therapeutic targeting of the E3 ubiquitin ligase SKP2 in T-ALL

Timed degradation of the cyclin-dependent kinase inhibitor p27^Kip1 by the E3 ubiquitin ligase F-box protein SKP2 is critical for T-cell progression into cell cycle, coordinating proliferation and differentiation processes. SKP2 expression is regulated by mitogenic stimuli and by Notch signaling, a key pathway in T-cell development and in T-cell acute lymphoblastic leukemia (T-ALL); however, it is not known whether SKP2 plays a role in the development of T-ALL. Here, we determined that SKP2 function is relevant for T-ALL leukemogenesis, whereas is dispensable for T-cell development. Targeted inhibition of SKP2 by genetic deletion or pharmacological blockade markedly inhibited proliferation of human T-ALL cells in vitro and antagonized disease in vivo in murine and xenograft leukemia models, with little effect on normal tissues. We also demonstrate a novel feed forward feedback loop by which Notch and IL-7 signaling cooperatively converge on SKP2 induction and cell cycle activation. These studies show that the Notch/SKP2/p27^Kip1 pathway plays a unique role in T-ALL development and provide a proof-of-concept for the use of SKP2 as a new therapeutic target in T-cell acute lymphoblastic leukemia (T-ALL).

Ex vivo culture of mouse skin activates an interleukin 1 alpha-dependent inflammatory response

Ex vivo culture of mouse and human skin causes an inflammatory response characterized by production of multiple cytokines. We used ex vivo culture of mouse tail skin specimens to investigate mechanisms of this skin culture-induced inflammatory response. Multiplex assays revealed production of interleukin 1 alpha (IL-1α), interleukin 1 beta (IL-1β), interleukin 6 (IL-6), chemokine C-X-C motif ligand 1 (CXCL1), granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) during skin culture, and quantitative PCR revealed transcripts for these proteins were also increased. Ex vivo cultures of skin from myeloid differentiation primary response 88 deficient mice (Myd88^-/- ) demonstrated significantly reduced expression of transcripts for the aforementioned cytokines. The same result was observed with skin from interleukin 1 receptor type 1 deficient mice (Il1r1^-/- ). These data suggested the IL-1R1/MyD88 axis is required for the skin culture-induced inflammatory response and led us to investigate the role of IL-1α and IL-1β (the ligands for IL-1R1) in this process. Addition of IL-1α neutralizing antibody to skin cultures significantly reduced expression of Cxcl1, Il6 and Csf3. IL-1β neutralization did not reduce levels of these transcripts. These studies suggest that IL-1α promotes the skin the culture-induced inflammatory response.

BATF-Interacting Proteins Dictate Specificity in Th Subset Activity

The basic leucine zipper (bZIP) transcription factor BATF is expressed in multiple Th subsets and cooperates with other factors to regulate gene transcription. BATF activates lineage-specific cytokines in Th subsets, activating IL-9 in Th9 cells and IL-17 in Th17 cells, but not IL-9 or IL-17 in the reciprocal subset. The mechanism for this restricted activity is unclear. In this report, we define BATF binding partners that contribute to Th subset-specific functions. Although BATF and IRF4 are expressed in greater amounts in Th9 than Th17, increased expression of both factors is not sufficient to induce IL-9 in Th17 cells. BATF also requires heterodimer formation with Jun family members to bind DNA and induce gene expression. Using primary mouse T cell culture, we observed that JunB and c-Jun, but not JunD, promote IL-9 production in Th9 cells. Ectopic expression of BATF with either JunB or c-Jun generates modest, but significant, increases in IL-9 production in Th17 cells, suggesting that the low expression of Jun family members is one factor limiting the ability of BATF to induce IL-9 in Th17 cells. We further identified that Bach2 positively regulates IL-9 production by directly binding to the Il9 gene and by increasing transcription factor expression in Th9 cells. Strikingly, cotransduction of Bach2 and BATF significantly induces IL-9 production in both Th9 and Th17 cells. Taken together, our results reveal that JunB, c-Jun, and Bach2 cooperate with BATF to contribute to the specificity of BATF-dependent cytokine induction in Th subsets.

The Transcription Factor Bhlhe40 Programs Mitochondrial Regulation of Resident CD8+ T Cell Fitness and Functionality

Tissue-resident memory CD8⁺ T (Trm) cells share core residency gene programs with tumor-infiltrating lymphocytes (TILs). However, the transcriptional, metabolic, and epigenetic regulation of Trm cell and TIL development and function is largely undefined. Here, we found that the transcription factor Bhlhe40 was specifically required for Trm cell and TIL development and polyfunctionality. Local PD-1 signaling inhibited TIL Bhlhe40 expression, and Bhlhe40 was critical for TIL reinvigoration following anti-PD-L1 blockade. Mechanistically, Bhlhe40 sustained Trm cell and TIL mitochondrial fitness and a functional epigenetic state. Building on these findings, we identified an epigenetic and metabolic regimen that promoted Trm cell and TIL gene signatures associated with tissue residency and polyfunctionality. This regimen empowered the anti-tumor activity of CD8⁺ T cells and possessed therapeutic potential even at an advanced tumor stage in mouse models. Our results provide mechanistic insights into the local regulation of Trm cell and TIL function.

The Il9 CNS-25 Regulatory Element Controls Mast Cell and Basophil IL-9 Production

IL-9 is an important mediator of allergic disease that is critical for mast cell-driven diseases. IL-9 is produced by many cell types, including T cells, basophils, and mast cells. Yet, how IL-9 is regulated in mast cells or basophils is not well characterized. In this report, we tested the effects of deficiency of a mouse Il9 gene regulatory element (Il9 CNS-25) in these cells in vivo and in vitro. In mast cells stimulated with IL-3 and IL-33, the Il9 CNS-25 enhancer is a potent regulator of mast cell Il9 gene transcription and epigenetic modification at the Il9 locus. Our data show preferential binding of STAT5 and GATA1 to CNS-25 over the Il9 promoter in mast cells and that T cells and mast cells have differing requirements for the induction of IL-9 production. Il9 CNS-25 is required for IL-9 production from T cells, basophils, and mast cells in a food allergy model, and deficiency in IL-9 expression results in decreased mast cell expansion. In a Nippostrongylus brasiliensis infection model, we observed a similar decrease in mast cell accumulation. Although decreased mast cells correlated with higher parasite egg burden and delayed clearance in vivo, T cell deficiency in IL-9 also likely contributes to the phenotype. Thus, our data demonstrate IL-9 production in mast cells and basophils in vivo requires Il9 CNS-25, and that Il9 CNS-25-dependent IL-9 production is required for mast cell expansion during allergic intestinal inflammation.

Roles of T Follicular Helper Cells and T Follicular Regulatory Cells in Autoantibody Production in IL-2-Deficient Mice

Autoantibodies can result from excessive T follicular helper (Tfh) cell activity, whereas T follicular regulatory (Tfr) cells negatively regulate autoantibody production. IL-2 knockout (KO) mice on the BALB/c background have elevated Tfh responses, produce autoantibodies, and develop lethal autoimmunity. We analyzed Tfh and Tfr cells in IL-2 KO mice on the C57BL/6 (B6) genetic background. In B6 IL-2 KO mice, the spontaneous formation of Tfh cells and germinal center B cells was greatly enhanced, along with production of anti-DNA autoantibodies. IL-2 has been reported to repress Tfr cell differentiation; however, Tfr cells were not increased over wild-type levels in the B6 IL-2 KO mice. To assess Tfh and Tfr cell regulation of autoantibody production in IL-2 KO mice, we generated IL-2 KO mice with a T cell-specific deletion of the master Tfh cell transcription factor Bcl6. In IL-2 KO Bcl6 conditional KO (2KO-Bcl6TC) mice, Tfh cells, Tfr cells, and germinal center B cells were ablated. In contrast to expectations, autoantibody IgG titers in 2KO-Bcl6TC mice were significantly elevated over autoantibody IgG titers in IL-2 KO mice. Specific deletion of Tfr cells with Foxp3-cre Bcl6-flox alleles in IL-2 KO mice led to early lethality, before high levels of autoantibodies could develop. We found IL-2^+/+ Tfr cell-deficient mice produce significant levels of autoantibodies. Our overall findings provide evidence that Tfh cells are dispensable for high-level production of autoantibodies and also reveal a complex interplay between Tfh and Tfr cells in autoantibody production and autoimmune disease.

Covalent Heterobivalent Inhibitor Design for Inhibition of IgE-Dependent Penicillin Allergy in a Murine Model

Drug allergies occur when hapten-like drug metabolites conjugated to serum proteins, through their interactions with specific IgE, trigger allergic reactions that can be life threatening. A molecule termed covalent heterobivalent inhibitor (cHBI) was designed to specifically target drug hapten-specific IgE to prevent it from binding drug-haptenated serum proteins. cHBI binds the two independent sites on a drug hapten-specific Ab and covalently conjugates only to the specific IgE, permanently inhibiting it. The cHBI design was evaluated via ELISA to measure cHBI-IgE binding, degranulation assays of rat basophil leukemia cells for in vitro efficacy, and mouse models of ear swelling and systemic anaphylaxis responses for in vivo efficacy. The cHBI design was evaluated using two separate models: one specific to inhibit penicillin G-reactive IgE and another to inhibit IgE specific to a model compound, dansyl. We show that cHBI conjugated specifically to its target Ab and inhibited degranulation in cellular degranulation assays using rat basophil leukemia cells. Furthermore, cHBIs demonstrated in vivo inhibition of allergic responses in both murine models. We establish the cHBI design to be a versatile platform for inhibiting hapten/IgE interactions, which can potentially be applied to inhibit IgE-mediated allergic reactions to any drug/small-molecule allergy.

Structural variation of centromeric endogenous retroviruses in human populations and their impact on cutaneous T-cell lymphoma, Sézary syndrome, and HIV infection

Background

Human Endogenous Retroviruses type K HML-2 (HK2) are integrated into 117 or more areas of human chromosomal arms while two newly discovered HK2 proviruses, K111 and K222, spread extensively in pericentromeric regions, are the first retroviruses discovered in these areas of our genome.

Methods

We use PCR and sequencing analysis to characterize pericentromeric K111 proviruses in DNA from individuals of diverse ethnicities and patients with different diseases.

Results

We found that the 5′ LTR-gag region of K111 proviruses is missing in certain individuals, creating pericentromeric instability. K111 deletion (−/− K111) is seen in about 15% of Caucasian, Asian, and Middle Eastern populations; it is missing in 2.36% of African individuals, suggesting that the −/− K111 genotype originated out of Africa. As we identified the −/−K111 genotype in Cutaneous T-cell lymphoma (CTCL) cell lines, we studied whether the −/−K111 genotype is associated with CTCL. We found a significant increase in the frequency of detection of the −/−K111 genotype in Caucasian patients with severe CTCL and/or Sézary syndrome (n = 35, 37.14%), compared to healthy controls (n = 160, 15.6%) [p = 0.011]. The −/−K111 genotype was also found to vary in HIV-1 infection. Although Caucasian healthy individuals have a similar frequency of detection of the −/− K111 genotype, Caucasian HIV Long-Term Non-Progressors (LTNPs) and/or elite controllers, have significantly higher detection of the −/−K111 genotype (30.55%; n = 36) than patients who rapidly progress to AIDS (8.5%; n = 47) [p = 0.0097].

Conclusion

Our data indicate that pericentromeric instability is associated with more severe CTCL and/or Sézary syndrome in Caucasians, and appears to allow T-cells to survive lysis by HIV infection. These findings also provide new understanding of human evolution, as the −/−K111 genotype appears to have arisen out of Africa and is distributed unevenly throughout the world, possibly affecting the severity of HIV in different geographic areas.

Electronic supplementary material

The online version of this article (10.1186/s12920-019-0505-8) contains supplementary material, which is available to authorized users.

BATF-interacting proteins dictate specificity in Th subset activity

The basic leucine zipper transcription factor BATF is expressed in multiple Th subsets and cooperates with other factors to regulate gene transcription. BATF activates lineage-specific cytokines in Th subsets, activating IL-9 in Th9 cells and IL-17 in Th17 cells. The mechanism for this restricted activity is unclear. In this report we define BATF binding partners that contribute to Th subset-specific functions. Although BATF and IRF4 are expressed in greater amounts in Th9 than Th17, increased expression of both factors is not sufficient to induce IL-9 in Th17 cells. BATF also requires heterodimer formation with Jun family members to bind DNA and induce gene expression. We observed that JunB and c-Jun, but not JunD, promote IL-9 production in Th9 cells. Ectopic expression of BATF with either JunB or c-Jun generates modest but significant increases in IL-9 production in Th17 cells, suggesting that the low expression of Jun family members is one factor limiting the ability of BATF to induce IL-9 in Th17 cells. We further identified that Bach2 positively regulates IL-9 production by directly binding to the Il9 gene and by increasing transcription factor expression in Th9 cells. Strikingly, co-transduction of Bach2 and BATF significantly induces IL-9 production in both Th9 and Th17 cell. Taken together, our results reveal that JunB, c-Jun and Bach2 cooperate with BATF to contribute to the specificity of BATF-dependent cytokine induction in Th subsets.

Role of Ets Transcription factors in the development of TH9 cells

T cells are critical regulators of inflammatory diseases and immunity. CD4+ T helper cells develop into various subsets that are specialized in the secretion of particular cytokines and mediate restricted types of inflammation. One of these subsets recently identified to play an important role in development of allergic inflammatory response, is the IL-9 producing TH9 subset. TH9 cells differentiate in the presence of IL-4 and TGFβ, which activate a network of transcription factors downstream of STAT6 and SMAD signaling pathways to regulate IL-9 secretion. Previous studies showed that PU.1, an Ets transcription factor, can bind at the Il9 promoter region to regulate TH9 function during pro-allergic inflammation. Furthermore, members of the Ets family of transcription factors Etv5 and PU.1 appear to share overlapping functions to promote IL-9 production and TH9 development. We screened for additional ETS factors that might play a role in IL-9 regulation. Jabeen et. al. showed the Ets transcription factor termed Erg (Ets-related gene) is expressed preferentially in TH9 subset. Accordingly, we determined that siRNA knock down of Erg in TH9 cells decreased IL-9 production in vitro. Moreover, chromatin immunoprecipitation assay demonstrated that Erg binding at the Il9 promoter and enhancer region is enriched in TH9 cells. Furthermore, ectopic expression of Erg induced IL-9 secretion in TH2 cells. In addition to Erg, we identified Fli-1, another Ets transcription factor, that can enhance IL-9 secretion in TH2 subset and whose expression is altered by Erg-deficiency. Thus, multiple Ets transcription factors regulate Il9 expression in TH9 cells, suggesting that Erg and other Ets transcription factors may cooperate to promote TH9 function.

IL-9-secreting tissue-resident memory CD4+ T cells contribute to allergic airway recall responses

Asthma is a chronic intermittent inflammatory lung disease for which there is no cure. Allergen-specific CD4 T helper (Th) cells that secrete cytokines including IL-4, IL-13, and IL-9 mediate asthma pathogenesis. In a six week chronic model of allergic airway disease, we were able to detect a robust IL-9+CD4+ T cell population in the lungs. Interestingly, the in vivo derived IL-9+CD4+ T cells had a multi-cytokine profile including the production of IL-5, IL-13, and IL-10. IL-9-reporter-positive cells demonstrated high gene expression levels of innate cytokine receptors Il1rl1, Il17rb, and Crlf2 and the transcription factor Gata3. IL-9+CD4+ T cells were found to be tissue-resident through intravenous labeling and had CD4+ tissue-resident memory (Trm) cell markers CD69 and CD11a. To determine the Trm phenotype of lung resident IL-9+ T cells, we developed a memory model using a five week period of rest after six weeks of chronic challenge, before a recall allergen challenge. In the memory model, IL-9+ T cells maintained tissue residency and demonstrated increased cell frequency and IL-9 production, characteristic of a secondary response. Antibody blockade of IL-9 immediately prior to the recall challenge significantly reduced overall allergic lung inflammation, suggesting that IL-9 plays an obligate role in the allergic memory response following pulmonary allergen challenge. These observations further suggest that IL-9 from Trm cell populations plays a novel role in allergen recall responses and is a potential therapeutic target for patients suffering from chronic intermittent asthma.

The IL-12/STAT4 pathway associates with critical functions in neutrophils

Signal transducer and activator of transcription 4 (STAT4) becomes activated via phosphorylation by JAK/Tyk kinases in response to IL-12 and other cytokines, which results in downstream transcription of pro-inflammatory genes. Our preliminary data are the first to demonstrate that IL-12 induces phospho-STAT4 in neutrophils. STAT4, JAK2, and p38 MAPK, but not Tyk2, become rapidly phosphorylated in response to IL-12 treatment in a time dependent manner. Pharmacologic inhibition of JAK1/2, but not p38, resulted in a two-fold reduction in phospho-STAT4, confirming its role as a signalling intermediate during STAT4 activation. Although IL-12 does not induce ROS formation in the short term (&lt;3 hours), we were surprised to discover a 4-fold increase in ROS production in response to long term IL-12 treatment (14 hrs), compared to only 1.5-fold increase in STAT4-deficient neutrophils. Additionally, we observed a dramatic 15-fold decrease in in vitro migration of STAT4-deficient neutrophils towards the chemoattractant GM-CSF compared to wild-type. Preliminary in vivo studies have revealed deficient migration to the peritoneal cavity of STAT4-deficient mice following intraperitoneal injection of GM-CSF. Finally, we demonstrate that in vitro NET formation in response to PMA treatment is impaired 5-fold in STAT4-deficient neutrophils compared to wild-type. These findings highlight the novel IL-12/STAT4 pro-inflammatory signalling pathway in murine neutrophils. Our data suggest a major contributory role of STAT4 in mediating neutrophil functions that have been previously associated with the progression of atherosclerosis. Future in vivo studies will determine the neutrophil-specific role of STAT4 in atherosclerotic mice.

Granzyme A-producing helper T cells are critical for lethal acute graft-versus-host disease

Graft-versus-host disease (GVHD) is a deleterious allo-immune response that occurs in patients undergoing hematopoietic stem cell transplantation (HSCT) for treatment of blood-derived malignancies. CD4 T helper (Th) cells within the donor HSC pool recognize allogeneic HLA molecules and traffic to multiple organs, including the intestines where increased inflammation correlates with worsened clinical prognosis. Despite the known role of Th cells in GVHD, the means by which they promote disease remain unclear. In our studies, we have identified a novel class of Th cells that produce the serine protease granzyme A (GrA) within the intestines of mice succumbing to GVHD. GrA+ Th cells were distinct from other Th lineages and largely lacked co-expression of other Th lineage-associated cytokines or cytolytic mediators. Importantly, mice that received HSCT with GrA-deficient CD4 T cells exhibited significantly reduced morbidity and mortality as compared to controls, suggesting that Th-derived GrA is critical for GVHD progression. In vitro, differentiation of GrA+ Th cells was optimally induced with a combination of IL-6, IL-21 and IL-4 in a STAT3- and STAT6-dependent fashion. In vivo, STAT3- was also partially required for the differentiation of GrA+ Th cells during the GVHD response. In summary, GrA+ Th cells represent a novel STAT3-dependent Th cell type that is critical for allo-immune mediated disease.

Defining the Phenotype and Function of Granzyme A Expressing T-Helper Cells

Granzymes have been implicated in numerous diseases including arthritis, viral and bacterial infections, hypersensitivity, autoimmune diabetes, and some cancers. In a STAT6 transgenic mouse model of atopic dermatitis, we identified a population of Granzyme A expressing CD4-T- cells. The role that these cells play in disease is unclear. To define their phenotype, we generated granzyme A (GrA)-expressing T helper cells in vitro using a combination of IL-4/IL-6 and IL-21. GrA-expressing TH cells did not express other TH subsetassociated cytokines, and other TH subsets did not appreciably express GrA. To further examine the development and function of GrA+ TH cells, we developed a Granzyme A-GFP reporter allele termed Grama (GrA Monitoring Allele) mouse. Grama+ cells were identified in the spleen and intestine. Using RNA-seq analysis of in vitro derived cells, we additionally identified several genes, including Arg1, Zpbp2, and Rpl39, that were enriched in GrA-expressing T cells. Thus, GrA-expressing CD4 T cells may represent a novel TH subset and it will be interesting to define the function of this subset in inflammatory diseases.

The Th2 cytokine IL-4 mediates loss of skin γδT cells in atopic dermatitis

Atopic dermatitis (AD) is a common Th2-biased chronic inflammatory skin disease. Major clinical manifestations include erythema, severe itchiness, and dry skin that impose a burden on patients and impairs their quality of life. Extensive research has been conducted to identify possible underlying mechanisms and develop therapeutic approaches. γδT cells, an understudied T cell population, play important roles in maintaining skin integrity in both human and mice. They are among the first responders to epithelial wounding and are a source of keratinocyte/fibroblast growth factors that promote wound repair. Hence, we wanted to investigate their behavior during wounding in an AD-like environment. Using a mouse model, we observed that γδT cell numbers are drastically decreased in atopic skin. Multiple factors contribute to this decrease, including insufficient activation, less proliferative capacity and increased cell death. These changes in γδT cell function are IL-4 dependent. Administration of IL-4 to wild type (WT) mice resulted in significant loss of γδT cells, and Il4−/− mice in the AD model showed numbers of γδT cells similar to WT controls. We further observed that the levels of keratinocyte/fibroblast growth factors are lower in AD animals, suggesting that loss of γδT cells could compromise re-epithelialization and repair following wounding. Collectively, our data indicate that in an atopic environment, γδT cells decrease drastically in an IL-4 dependent fashion, which may contribute to the aberrant wound healing process in AD animals.

Endonuclease and redox activities of human apurinic/apyrimidinic endonuclease 1 have distinctive and essential functions in IgA class switch recombination

The base excision repair (BER) pathway is an important DNA repair pathway and is essential for immune responses. In fact, it regulates both the antigen-stimulated somatic hypermutation (SHM) process and plays a central function in the process of class switch recombination (CSR). For both processes, a central role for apurinic/apyrimidinic endonuclease 1 (APE1) has been demonstrated. APE1 acts also as a master regulator of gene expression through its redox activity. APE1's redox activity stimulates the DNA-binding activity of several transcription factors, including NF-κB and a few others involved in inflammation and in immune responses. Therefore, it is possible that APE1 has a role in regulating the CSR through its function as a redox coactivator. The present study was undertaken to address this question. Using the CSR-competent mouse B-cell line CH12F3 and a combination of specific inhibitors of APE1's redox (APX3330) and repair (compound 3) activities, APE1-deficient or -reconstituted cell lines expressing redox-deficient or endonuclease-deficient proteins, and APX3330-treated mice, we determined the contributions of both endonuclease and redox functions of APE1 in CSR. We found that APE1's endonuclease activity is essential for IgA-class switch recombination. We provide evidence that the redox function of APE1 appears to play a role in regulating CSR through the interleukin-6 signaling pathway and in proper IgA expression. Our results shed light on APE1's redox function in the control of cancer growth through modulation of the IgA CSR process.