Elevated Antigen-Driven IL-9 Responses Are Prominent in Peanut Allergic Humans

Abstract

Food allergies, and peanut allergy in particular, are leading causes of anaphylactic fatalities worldwide. The immune mechanisms that underlie food allergy remain ill-defined and controversial, in part because studies in humans typically focus on analysis of a limited number of prototypical Th1/Th2 cytokines. Here we determine the kinetics and prevalence of a broad panel of peanut-driven cytokine and chemokine responses in humans with current peanut allergy vs those with stable, naturally occurring clinical tolerance to peanut. Our primary focus is identification of novel indicators of immune dysregulation. Antigen-specific cytokine mRNA and protein responses were elicited in primary culture via peanut or irrelevant antigen (Leishmania extract, milk antigens) mediated stimulation of fresh peripheral blood cells from 40 individuals. Peanut extract exposure in vitro induced a broad panel of responses associated with Th2/Th9-like, Th1-like and Th17-like immunity. Peanut-dependent Type 2 cytokine responses were frequently found in both peanut allergic individuals and those who exhibit clinical tolerance to peanut ingestion. Among Th2/Th9-associated cytokines, IL-9 responses discriminated between allergic and clinically tolerant populations better than did commonly used IL-4, IL-5 or IL-13 responses. Comparison with responses evoked by unrelated control antigen-mediated stimulation showed that these differences are antigen-dependent and allergen-specific. Conversely, the intensity of IL-12, IL-17, IL-23 and IFN-γ production was indistinguishable in peanut allergic and peanut tolerant populations. In summary, the ability to generate and maintain cytokine responses to peanut is not inherently distinct between allergic and peanut tolerant humans. Quantitative differences in the intensity of cytokine production better reflects clinical phenotype, with optimally useful indicators being IL-9, IL-5, IL-13 and IL-4. Equivalent, and minimal, Ag-dependent pro-inflammatory cytokine levels in both healthy and peanut allergic volunteers argues against a key role for such cytokines in maintenance of clinical tolerance to food antigens in humans.

Markers of tolerance development to food allergens

“…They demonstrated a significant upregulation of this cytokine among other TH2-type cytokines in peanut-specific activated gut and skin homing memory T-cell populations (127). This finding corresponds with data from peanut-stimulated PBMCs (128). To attribute a role of the TH9 subset in peanut allergy is interesting; however, more data are required.…”

Human Vδ2 T cells are a major source of interleukin-9

“…In the presence of TGF-β, the proliferative activity of freshly isolated γδ T cells as measured by 3 H-radiolabeled thymidine incorporation was reduced (Fig. S1A).…”

“…IL-9 is a pleiotropic cytokine that promotes T-cell and mast-cell growth and mast-cell accumulation in tissue as well as IgE switching in B cells (1). In line, allergic patients have increased numbers of T cells that produce IL-9 in response to various allergens (2,3). Moreover, Th9 cells alter intestinal epithelial cell functions (4,5) and are key players in antiworm immunity (6).…”

Mucosal Eosinophils

“…Notably, these symptoms are blocked by anti-IgE therapy or mast cell depletion (Mathias et al, 2011), strongly implicating mast cells with these cardinal features of eosinophilic GI diseases (Furuta et al, 2008;Brandt et al, 2003). Using this model system, the novel involvement of IL-9 in GI inflammation/anaphylaxis was recently identified (Osterfeld et al, 2010), indicating the critical role of IL-9 (secreted by Th9 cells) in GI allergic inflammation and associated anaphylaxis (Xie et al, 2012;Stassen et al, 2012).…”