EBV-induced gene 3 (EBI3) can associate with p28 to form the heterodimeric cytokine IL-27, or with the p35 subunit of IL-12 to form the EBI3/p35 heterodimer, recently named IL-35. In mice, IL-35 has been shown to be constitutively expressed by CD4+CD25+Foxp3+ regulatory T cells (Treg cells) and suggested to contribute to their suppressive activity. In this study, we investigated whether human Treg cells express IL-35. Double-staining analysis of human thymuses showed that neither Foxp3+ nor CD25+ cells coexpressed EBI3. Similarly, Foxp3+ cells present in human lymph nodes, tonsils, spleens, and intestines did not express EBI3. Consistent with these in situ observations, Treg cells purified from blood or tonsils were negative for EBI3 by immunoblotting. Other human T cell subsets, including effector T cells, naive and memory CD4+ T cells, CD8+ and γδ T cells also did not constitutively express EBI3, which contrasts with IL-35 expression observed in murine CD8+ and γδ T cells. Furthermore, although CD3/CD28 stimulation consistently induced low levels of EBI3 in various CD4+ T cell subsets, no EBI3 could be detected in CD3/CD28-stimulated Treg cells. RT-PCR analysis showed that, whereas p35 transcripts were detected in both Teff and Treg cells, EBI3 transcripts were detected only in activated Teff cells, but not in resting or activated Treg cells. Thus, in contrast to their murine counterpart, human Treg cells do not express detectable amounts of IL-35.

BackgroundInfections may be associated with exacerbation of allergic and autoimmune diseases. Paradoxically, epidemiological and experimental data have shown that some microorganisms can also prevent these pathologies. This observation is at the origin of the hygiene hypothesis according to which the decline of infections in western countries is at the origin of the increased incidence of both Th1-mediated autoimmune diseases and Th2-mediated allergic diseases over the last decades. We have tested whether Toll-like receptor (TLR) stimulation can recapitulate the protective effect of infectious agents on allergy and autoimmunity.Methods and FindingsHere, we performed a systematic study of the disease-modifying effects of a set of natural or synthetic TLR agonists using two experimental models, ovalbumin (OVA)-induced asthma and spontaneous autoimmune diabetes, presenting the same genetic background of the non obese diabetic mouse (NOD) that is highly susceptible to both pathologies. In the same models, we also investigated the effect of probiotics. Additionally, we examined the effect of the genetic invalidation of MyD88 on the development of allergic asthma and spontaneous diabetes. We demonstrate that multiple TLR agonists prevent from both allergy and autoimmunity when administered parenterally. Probiotics which stimulate TLRs also protect from these two diseases. The physiological relevance of these findings is further suggested by the major acceleration of OVA-induced asthma in MyD88 invalidated mice. Our results strongly indicate that the TLR-mediated effects involve immunoregulatory cytokines such as interleukin (IL)-10 and transforming growth factor (TGF)-β and different subsets of regulatory T cells, notably CD4+CD25+FoxP3+ T cells for TLR4 agonists and NKT cells for TLR3 agonists.Conclusions/SignificanceThese observations demonstrate that systemic administration of TLR ligands can suppress both allergic and autoimmune responses. They provide a plausible explanation for the hygiene hypothesis. They also open new therapeutic perspectives for the prevention of these pathologies.