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Intestinal helminth parasites can alter immune responses to vaccines, other infections, allergens and autoantigens, indicating effects on host immune responses in distal barrier tissues. We herein show that C57BL/6 mice infected with the strictly intestinal nematode Heligmosomoides polygyrus have impaired capacity to initiate skin immune responses and develop skin-resident memory cells to mycobacterial antigens, both during infection and months after deworming therapy. Surprisingly, and in contrast to a previously noted loss of T cells in peripheral lymph nodes, the skin of worm-infected mice harboured higher numbers of CD4+ T cells compared to skin of uninfected controls. H. polygyrus-specific TH2 cells accumulated during infection and remained after worm expulsion. Accumulation of TH2 cells in the skin was associated with increased expression of the skin-homing chemokine receptors CCR4 and CCR10 on CD4+ T cells in blood and mesenteric lymph nodes draining intestinal tissues, indicating gut-to-skin trafficking of cells. In conclusion, we show that infection by a strictly intestinal helminth has long-term effects on immune cell composition and local immune responses to unrelated antigens in the skin, revealing a novel mechanism for T cell colonization and worm-mediated immunosuppression in this organ.

Allergic disorders are caused by a combination of hereditary and environmental factors. The hygiene hypothesis postulates that early life microbial exposures impede the development of subsequent allergic disease. However, unambiguous evidence that microbes reduce the development of allergic disorders is still lacking. Recently developed ‘wildling’ mice contain a rich and diverse commensal and encounter a repertoire of microbes typical of the wild, with pathogenic potential. Here, we probed the hygiene hypothesis by comparing the development of allergic inflammation in wildlings to that of genetically identical mice lacking diverse microbial exposure. We find that wildlings develop stronger allergic inflammation in response to house dust mites with allergic T cell responses driven not only by cognate peptide antigens, but also by innate cytokines. In all, the results suggest that high microbial content and diversity potentiates, rather than restricts, allergic immune responses.One sentence summaryStrong allergic inflammation in the face of rich and diverse microbial exposures

Psoriasis is driven by focal disruptions of the immune-homeostasis in human skin. Local relapse following cessation of therapy is common and unpredictable, which complicates clinical management of psoriasis. We have previously shown that pathogenic resident T cells accumulate in active and resolved psoriasis, but whether these cells drive psoriasiform tissue reactions is less clear. Here, we activated T cells within skin explants using the pan-T cell activating antibody OKT-3. To explore if T cells induced different tissue response patterns in healthy and psoriasis afflicted skin, transcriptomic analyses were performed with RNA-sequencing and Nanostring. Core tissue responses dominated by IFN-induced pathways were triggered regardless of the inflammatory status of the skin. In contrast, pathways induced by IL-17A, including Defensin beta 2 and keratinocyte differentiation markers, were activated in psoriasis samples. An integrated analysis of IL-17A and IFN-related responses revealed that IL-17 dominated tissue response correlated with early relapse following UVB treatment. Stratification of tissue responses to T cell activation in resolved lesions could potentially offer individualized prediction of disease relapse during long-term immunomodulatory treatment.

Intestinal nematodes suppress immune responses in the context of allergy, gut inflammation, secondary infection and vaccination. Several mechanisms have been proposed for this suppression including alterations in Th2 cell differentiation and increased Treg cell suppressive function. In this study, we show that chronic nematode infection leads to reduced peripheral responses to vaccination because of a generalized reduction in the available responsive lymphocyte pool. We found that superficial skin-draining lymph nodes (LNs) in mice that are chronically infected with the intestinal nematode Heligmosomides polygyrus, do not reach the same cellularity as worm-free mice upon subsequent BCG infection in the skin. B cells and T cells, all declined in skin-draining LN of H. polygyrus-infected mice, resulting in LNs atrophy and altered lymphocyte composition. Importantly, anti-helminthic treatment improved lymphocyte numbers in skin-draining LN, indicating that time after de-worming is critical to regain full-scale LN cellularity. De-worming, and time for the skin LN to recover cellularity, also mended responses to Bacille Calmette-Guerin (BCG) in the LN draining the footpad injection site. Thus, our findings show that chronic nematode infection leads to a paucity of lymphocytes in peripheral lymph nodes, which acts to reduce the efficacy of immune responses at these sites., Author summary Infections with intestinal nematodes may be one explanation to why BCG vaccination is less effective in areas of high worm burden. In support of this, we recently showed that chronic intestinal nematode infection resulted in reduced immune responses and higher mycobacterial burden at distal sites. How a gut-dwelling nematode modulate immune responses in skin-draining lymph nodes (LN) was not clear. We found a reduced expansion of LN draining the BCG injected footpad in worm-infected animals, but no evidence for a spread of regulatory cells or cytokines to the BCG-draining LN. Interestingly, we found that mice chronically infected with intestinal worms had significantly smaller skin-draining LN. We propose that the expansion of mesenteric lymph nodes (mLN) occur at the cost of other LN, leading to atrophy of skin-draining LN. Expansion of the lymphocyte pool by IL-7, allowed worm-infected animals to maintain larger skin-draining LN while the mLN did not further expand. De-worming treatment of mice eventually restored the cellularity of skin-draining LN. This, however, took time indicating that effect of worms persisted long after the infection cleared. By de-worming and allowing time for the LN to recover, the cellular responses to BCG injection in the footpad were restored in the draining popliteal LN. Thus, paucity of lymphocytes at peripheral sites can explain impaired peripheral immune responses in worm-infected animals.

STAT3 is a master regulator of the immune responses. Here we show that M. tuberculosis-infected stat3fl/fl lysm cre mice, defective for STAT3 in myeloid cells, contained lower bacterial load in lungs and spleens, reduced granuloma extension but higher levels of pulmonary neutrophils. STAT3-deficient macrophages showed no improved control of intracellular mycobacterial growth. Instead, protection associated to elevated ability of stat3fl/fl lysm cre antigen-presenting cells (APCs) to release IL-6 and IL-23 and to stimulate IL-17 secretion by mycobacteria-specific T cells. The increased IL-17 secretion accounted for the improved control of infection since neutralization of IL-17 receptor A in stat3fl/fl lysm cre mice hampered bacterial control. APCs lacking SOCS3, which inhibits STAT3 activation via several cytokine receptors, were poor inducers of priming and of the IL-17 production by mycobacteria-specific T cells. In agreement, socs3fl/fl cd11c cre mice deficient of SOCS3 in DCs showed increased susceptibility to M. tuberculosis infection. While STAT3 in APCs hampered IL-17 responses, STAT3 in mycobacteria-specific T cells was critical for IL-17 secretion, while SOCS3 in T cells impeded IL-17 secretion. Altogether, STAT3 signalling in myeloid cells is deleterious in the control of infection with M. tuberculosis., Author summary We studied the role of STAT3, a major regulator of immunity, in the control of the infection with M. tuberculosis. Stat3fl/fl lysm cre mice, deficient in STAT3 in myeloid cells, showed lower bacterial levels in organs and reduced extension of lung granulomas after infection with M. tuberculosis. STAT3-deficient APCs stimulated with innate receptor agonists released high levels of IL-6 and IL-23, and promoted IL-17 production by mycobacteria-specific CD4+ T cells. Increased IL-17 levels accounted for the increased resistance to M. tuberculosis of the STAT3-deficient mice. Instead, stat3fl/fl lysm cre macrophages showed no improved control of mycobacterial growth. SOCS3 is a negative regulator of STAT3 activation. The ability of socs3fl/fl lysm cre APCs to secrete IL-6 and IL-23 and to stimulate IL-17 production by antigen-specific T cells was reduced. In agreement, mice lacking SOCS3 in DCs showed increased susceptibility to M. tuberculosis infection. Different to a role in myeloid cells, STAT3 expression by mycobacteria-specific T cells was required for IL-17 secretion while SOCS3 in T cells hampered IL-17 production. Therefore, despite STAT3 expression in T cells is required for Th17 differentiation, STAT3 in APCs hampers secretion of Th17 promoting cytokines and the secretion of IL-17 by mycobacteria-specific T cells and reduces the resistance of mice to infection with M. tuberculosis.

Leishmania donovani exposure often results in subclinical infection in immunocompetent individuals, and the factors dictating development of visceral leishmaniasis (VL) are not known. Infection with intestinal worms skew immunity towards type 2 and regulatory responses, thereby theoretically increases susceptibility to intracellular infections controlled by type 1 responses. Here we have tested how chronic infection with the intestinal nematode Heligmosomoides polygyrus affected immunity to a secondary infection with L donovani. We found that mice infected with H polygyrus displayed higher Leishmania burden in liver and spleen compared to worm-free animals. This increased infectious load was accompanied by reduced leucocyte infiltration and nos2 transcription in livers and increased il4 and il10 transcription in spleens. Collectively, these data show that chronic infection with intestinal nematodes skew immune responses in a way that may favour development of VL.

Helminth infections have been suggested to impair the development and outcome of Th1 responses to vaccines and intracellular microorganisms. However, there are limited data regarding the ability of intestinal nematodes to modulate Th1 responses at sites distal to the gut. In this study, we have investigated the effect of the intestinal nematode Heligmosomoides polygyrus bakeri on Th1 responses to Mycobacterium bovis bacillus Calmette–Guérin (BCG). We found that H. polygyrus infection localized to the gut can mute BCG-specific CD4+ T cell priming in both the spleen and skin-draining lymph nodes. Furthermore, H. polygyrus infection reduced the magnitude of delayed-type hypersensitivity (DTH) to PPD in the skin. Consequently, H. polygyrus–infected mice challenged with BCG had a higher mycobacterial load in the liver compared with worm-free mice. The excretory–secretory product from H. polygyrus (HES) was found to dampen IFN-γ production by mycobacteria-specific CD4+ T cells. This inhibition was dependent on the TGF-βR signaling activity of HES, suggesting that TGF-β signaling plays a role in the impaired Th1 responses observed coinfection with worms. Similar to results with mycobacteria, H. polygyrus–infected mice displayed an increase in skin parasite load upon secondary infection with Leishmania major as well as a reduction in DTH responses to Leishmania Ag. We show that a nematode confined to the gut can mute T cell responses to mycobacteria and impair control of secondary infections distal to the gut. The ability of intestinal helminths to reduce DTH responses may have clinical implications for the use of skin test–based diagnosis of microbial infections.

Introduction Le psoriasis est une maladie inflammatoire cutanee chronique. Dans les lesions apres traitement, en remission macroscopique, la signature moleculaire n’est cependant pas totalement normalisee. Les lymphocytes T memoires cutanes (TRM) qui resident dans la peau en remission du psoriasis produisent plus d’IL-17 et d’IL-22 que dans la peau des controles sains, et pourraient constituer l’origine cellulaire des anomalies transcriptomiques du psoriasis en remission. L’impact direct de ces cellules sur le tissu cutane environnant reste cependant a etudier : l’activation des TRM est-elle suffisante pour entrainer une recidive locale du psoriasis ? Nous presentons ici la reponse tissulaire a l’activation lymphocytaire dans des biopsies de patients. Materiel et methodes Des biopsies cutanees ont ete prelevees sur des controles sains, des patients avec psoriasis actif (n = 10) et en remission (biotherapies n = 9, UVB n = 9 et PUVA n = 5). L’activation des lymphocytes Tetait obtenue par exposition des biopsies a un anticorps anti-CD3 (OKT3 1 μg/mL) compare a un controle (isotype IgG2a 1 μg/mL). Apres 16 heures d’incubation, une separation enzymatique du derme et de l’epiderme etait effectuee et l’ARN etait extrait apres homogeneisation des tissus par le TissueLyser (Qiagen). Des analyses transcriptomiques etaient effectuees par RT-PCR, Nanostring et sequencage d’ARN messager. La secretion cytokinique etait analysee par Luminex et la microscopie etait realisee par imagerie confoncale (Zeiss LSM800). Resultats Dans tous les groupes (lesions actives, en remission ou controles) et avec les trois methodes transcriptomiques utilisees, une augmentation d’IFNγet des genes keratinocytaires d’aval (CXCL10, CXCL9) etait trouvee apres activation lymphocytaire. Un signal IL17etait aussi augmente (DefB2, SPRR2), plus dans les lesions actives et en remission sous biotherapie que dans la peau saine. Pour etudier l’interet clinique de l’equilibre entre ces deux reponses, la meme experience etait realisee sur une cohorte de 9 patients apres traitement par UVB. Dans les biopsies de leur peau en remission, une reponse en faveur d’IL-17 plutot qu’IFNγ apres activation lymphocytaire etait correle a une recidive clinique plus precoce (p Discussion Ce model ex vivo d’activation lymphocytaire de biopsies, isolees de la circulation sanguine, permet une description precise des equilibres cytokiniques au sein de la peau humaine. Dans le psoriasis, la presence d’un desequilibre en faveur de la production d’IL-17 apres traitement par UVB semble etre un facteur predisposant a la recidive. Conclusion La reponse cutanee a l’activation locale des lymphocytes T pourrait permettre une stratification des patients afin de predire leur reponse aux traitements.