The increased frequency of peripheral Th17 cells and serum IL-17 levels are shown in childhood HSP that may in part contribute to vascular inflammation, suggesting cellular immunity is likely to be involved in the process of HSP.

SummaryT helper type 2 (Th2) cells, which produce interleukin-4 (IL-4), IL-5 and IL-13, control immunity to all forms of allergic inflammatory responses. Interleukin-21 (IL-21) reduces allergic symptoms in murine models and inhibits IL-4-induced IgE secretion by B cells. However, whether or not IL-21 directly affects Th2 cells, which leads to reduced allergic symptoms, is unclear. In this study, we investigated the effects of IL-21 on the differentiation and effector functions of Th2 cells. We found that IL-21 reduced the number of differentiated Th2 cells and these Th2 cells showed a diminished Th2 cytokine production. Interleukin-21 suppressed Th2 cytokine production of already polarized Th2 cells by down-regulation of transcription factor GATA-3. It also induced apoptosis of Th2 cells with decreased anti-apoptotic factor Bcl-2. Intranasal administration of IL-21 at the beginning of ovalbumin (OVA) sensitization or before OVA challenge decreased Th2 cytokines in the bronchoalveolar lavage fluid of OVA/alum-immunized allergic mice. In addition, the inhibitory effects of IL-21 on Th2 effector functions can also be found in allergic patients. Our results demonstrate that IL-21 suppresses the development of Th2 cells and functions of polarized Th2 cells. Hence, the administration of IL-21 may be considered for use as a preventive and therapeutic approach when dealing with Th2-mediated allergic diseases.

Invariant NKT (iNKT) cells bridge innate and adaptive immune responses, resulting in the expansion of Ag-specific B and T cell responses. α-Galactosylceramide (α-GalCer), the most studied glycolipid that activates iNKT cells, has been proposed to be an effective adjuvant against infections and tumors. We found that the activation of iNKT cells by intranasal injection of α-GalCer induced airway eosinophilia in naive mice. Eosinophils, which mediate tissue damage and dysfunction by secreting mediators, play important roles in the pathogenesis of allergic diseases. In this study, we investigated the mechanism of how eosinophils are recruited to the lung by α-GalCer. Our results demonstrated that α-GalCer–induced eosinophil inflammation was mediated through iNKT cells. These cells secreted IL-5 to recruit eosinophils directly to the lung and/or secreted IL-4 and IL-13 to recruit eosinophils indirectly by inducing lung epithelial cells, endothelial cells, and fibroblast to secrete the eosinophil chemoattractant eotaxin. In addition, in the OVA-alum murine model of allergic asthma, α-GalCer administration in OVA-immunized mice also increased airway eosinophilia after challenge. Given our findings, intranasal administration of α-GalCer induced airway eosinophilic inflammation in both naive and allergic mice. Hence, it remains to be determined whether the activation of iNKT cells would be applicable in therapeutics for human diseases.

Allergic diseases, such as allergic rhinitis, caused by an immunoglobulin E (IgE)-mediated reaction to specific allergens are a common chronic condition worldwide. Interleukin-21 (IL-21), a type I cytokine that is produced by T cells, exerts regulatory effects on a variety of immune cells. In our previous study, we found that serum levels of IL-21 were significantly decreased in patients with severe atopic dermatitis, suggesting that IL-21 might play a role in allergic reactions. In this study, we investigated the role of IL-21/IL-21 receptor (IL-21R) in patients with allergic rhinitis. Our results demonstrated that there was no difference in IL-21 serum levels between allergic rhinitis patients and controls. However, allergic patients had significantly increased expression of IL-21R on naive and memory B cells. IL-21R was upregulated through stimulation by the combination of CD40 ligand (CD40L) and IL-4. IL-21 alone neither induced nor inhibited IgE secretion from CD40L-stimulated B cells. However, IL-21 inhibited IgE secretion of B cells that were induced by the combination of CD40L and IL-4 in allergic patients. Moreover, a negative correlation between the expression of IL-21R and serum levels of IgE was found in patients with allergy. These results suggest that the role of IL-21 in an ongoing allergic reaction is to downregulate the IgE level by binding to IL-21R on B cells, which increases the expression in allergic patients.