Mast cell-derived IL-13 downregulates IL-12 production by skin dendritic cells to inhibit the TH1 cell response to cutaneous antigen exposure.

BACKGROUND: Atopic dermatitis (AD) is characterized by a skin barrier defect aggravated by mechanical injury inflicted by scratching, a TH2 cell-dominated immune response, and susceptibility to viral skin infections that are normally restrained by a TH1 cell response. The signals leading to a TH2 cell-dominated immune response in AD are not completely understood. OBJECTIVE: Our aim was to determine the role of IL-13 in initiation of the TH cell response to cutaneously encountered antigens. METHODS: Wild-type, Il13-/-, Il1rl1-/-, and Il4ra-/- mice, as well as mice with selective deficiency of IL-13 in mast cells (MCs) were studied; in addition, dendritic cells (DCs) purified from the draining lymph nodes of tape-stripped and ovalbumin (OVA)-sensitized skin were examined for their ability to polarize naive OVA-TCR transgenic CD4+ T cells. Cytokine expression was examined by reverse-transcriptase quantitative PCR, intracellular flow cytometry, and ELISA. Contact hypersensitivity to dinitrofluorobenzene was examined. RESULTS: Tape stripping caused IL-33-driven upregulation of Il13 expression by skin MCs. MC-derived IL-13 acted on DCs from draining lymph nodes of OVA-sensitized skin to selectively suppress their ability to polarize naive OVA-TCR transgenic CD4+ T cells into IFN-γ-secreting cells. MC-derived IL-13 inhibited the TH1 cell response in contact hypersensitivity to dinitrofluorobenzene. IL-13 suppressed IL-12 production by mouse skin-derived DCs in vitro and in vivo. Scratching upregulated IL13 expression in human skin, and IL-13 suppressed the capacity of LPS-stimulated human skin DCs to express IL-12 and promote IFN-γ secretion by CD4+ T cells. CONCLUSION: Release of IL-13 by cutaneous MCs in response to mechanical skin injury inhibits the TH1 cell response to cutaneous antigen exposure in AD.

TH1 signatures are present in the lower airways of children with severe asthma, regardless of allergic status.

BACKGROUND: The pathogenesis of severe asthma in childhood remains poorly understood. OBJECTIVE: We sought to construct the immunologic landscape in the airways of children with severe asthma. METHODS: Comprehensive analysis of multiple cell types and mediators was performed by using flow cytometry and a multiplex assay with bronchoalveolar lavage (BAL) specimens (n = 68) from 52 highly characterized allergic and nonallergic children (0.5-17 years) with severe treatment-refractory asthma. Multiple relationships were tested by using linear mixed-effects modeling. RESULTS: Memory CCR5+ TH1 cells were enriched in BAL fluid versus blood, and pathogenic respiratory viruses and bacteria were readily detected. IFN-γ+IL-17+ and IFN-γ-IL-17+ subsets constituted secondary TH types, and BAL fluid CD8+ T cells were almost exclusively IFN-γ+. The TH17-associated mediators IL-23 and macrophage inflammatory protein 3α/CCL20 were highly expressed. Despite low TH2 numbers, TH2 cytokines were detected, and TH2 skewing correlated with total IgE levels. Type 2 innate lymphoid cells and basophils were scarce in BAL fluid. Levels of IL-5, IL-33, and IL-28A/IFN-λ2 were increased in multisensitized children and correlated with IgE levels to dust mite, ryegrass, and fungi but not cat, ragweed, or food sources. Additionally, levels of IL-5, but no other cytokine, increased with age and correlated with eosinophil numbers in BAL fluid and blood. Both plasmacytoid and IgE+FcεRI+ myeloid dendritic cells were present in BAL fluid. CONCLUSIONS: The lower airways of children with severe asthma display a dominant TH1 signature and atypical cytokine profiles that link to allergic status. Our findings deviate from established paradigms and warrant further assessment of the pathogenicity of TH1 cells in patients with severe asthma.

Interleukin-12: Functional activities and implications for disease.

Interleukin-12 (IL-12) was the first member of the IL-12 family of cytokines to be identified and has therefore become its eponym. It is a heterodimeric protein of two subunits (p35, p40) secreted by phagocytic cells in response to pathogens and mainly acts through STAT4 to induce IFN-γ production in T and NK cells. IFN-γ in turn mediates proinflammatory functions and activates T-bet. As IL-12 engages in TH1 development, it is believed to represent an important link between innate and adaptive immunity. Following its identification and the finding of its association to TH1 commitment, great hopes were placed in IL-12 to become a target for therapeutic applications in multiple settings of autoimmunity and cancer. Though, the discovery of the related members of the IL-12 family and several rather disappointing attempts to translate experimental results into clinical practice, have relativized these hopes. Nevertheless, IL-12 remains a cytokine of outstanding importance with lots of unresolved questions. In this review, we will first briefly depict the biochemistry of the cytokine, its receptor and the related signal transduction, before summarizing the regulation of IL-12 production and its biological functions. We will then describe the current knowledge about the implication of IL-12 in different murine disease models as well as in the corresponding human conditions and comment on possible consequences for future clinical applications.

Adoptive transfer of CD4(+)Foxp3(+) regulatory T cells to C57BL/6J mice during acute infection with Toxoplasma gondii down modulates the exacerbated Th1 immune response.

Infection of C57BL/6J mice with the parasite Toxoplasma gondii triggers a powerful Th1 immune response that is detrimental to the host. During acute infection, a reduction in CD4(+)Foxp3(+) regulatory T cells (Treg) has been reported. We studied the role of Treg during T. gondii infection by adoptive transfer of cells purified from transgenic Foxp3(EGFP) mice to infected wild type animals. We found a less severe weight loss, a significant delayed mortality in infected Treg-transferred mice, and reduced pathology of the small intestine that were associated with lower IFN-γ and TNF-α levels. Nevertheless, higher cyst number and parasite load in brain were observed in these mice. Treg-transferred infected mice showed reduced levels of both IFN-γ and TNF-α in sera. A reduced number of CD4(+) T cells producing IFN-γ was detected in these mice, while IL-2 producing CD4(+) T cells were restored to levels nearly similar to uninfected mice. CD25 and CD69 expression of CD4(+) T cells were also down modulated. Our data show that the low Treg cell number are insufficient to modulate the activation of CD4(+) T cells and the production of high levels of IFN-γ. Thus, a delicate balance between an optimal immune response and its modulation by Treg cells must exist.