There is great interest in tumor stem cells (TSCs) as potential therapeutic targets; however, cancer therapies targeting TSCs are limited. A drawback is that TSC markers are often shared by normal stem cells (NSCs); thus, therapies that target these markers may cause severe injury to normal tissues. To identify a potential TSC-specific marker, we focused on doublecortin-like kinase 1 (Dclk1). Dclk1 was reported as a candidate NSC marker in the gut, but recent reports have implicated it as a marker of differentiated cells (for example, Tuft cells). Using lineage-tracing experiments, we show here that Dclk1 does not mark NSCs in the intestine but instead marks TSCs that continuously produce tumor progeny in the polyps of Apc(Min/+) mice. Specific ablation of Dclk1-positive TSCs resulted in a marked regression of polyps without apparent damage to the normal intestine. Our data suggest the potential for developing a therapy for colorectal cancer based on targeting Dclk1-positive TSCs.

Cutaneous sensitization with a food antigen before its consumption elicits the development of food allergy. Here, we report the site- and stage-dependent roles of basophils and proallergic cytokines, thymic stromal lymphopoietin (TSLP) and IL-33, in a mouse model of food allergy initially sensitized cutaneously with the food antigen. Mice were epicutaneously sensitized with the food antigen ovalbumin (OVA) followed by oral challenge with OVA. Epicutaneously sensitized mice produced OVA-specific IgE and developed IgE-dependent anaphylaxis after oral challenge. Basophil-depleted or TSLP-receptor-deficient mice did not produce OVA-specific IgE and were protected from oral challenge-induced anaphylaxis. IL-33-deficient mice produced normal levels of OVA-specific IgE. However, IL-33-deficient mice and mice treated with recombinant soluble IL-33 receptor were protected from anaphylaxis. Thus, basophils and TSLP have pivotal roles in Th2 development in the skin during the sensitization phase of food allergy. In contrast, while IL-33 is dispensable for promoting cutaneous antigen sensitization, the cytokine is essential for inducing IgE-dependent anaphylaxis in the gut.

Thymic stromal lymphopoietin (TSLP) and IL-33 are epithelium-derived proallergic cytokines that contribute to allergic diseases. Although the involvement of TSLP in allergic rhinitis (AR) is suggested, the exact role of TSLP in AR is poorly understood. Furthermore, the relative contribution of TSLP and IL-33 in nasal allergic responses has not been described. In this study, we examined the roles of TSLP and IL-33 in AR by analyzing acute and chronic AR models. Acute AR mice were intraperitoneally immunized with ragweed, then intranasally challenged with ragweed pollen for four consecutive days. Chronic AR mice were nasally administrated ragweed pollen on consecutive days for 3 weeks. In both models, TSLP receptor (TSLPR)-deficient mice showed defective sneezing responses and reduced serum ragweed-specific IgE levels compared with wild-type (WT) mice. Analyses of bone-marrow chimeric mice demonstrated that hematopoietic cells were responsible for defective sneezing in TSLPR-deficient mice. In addition, FcεRI(+)-cell-specific TSLPR-deficient mice showed partial but significant reduction in sneezing responses. Of note, Th2 activation and nasal eosinophilia were comparable between WT and TSLPR-deficient mice. ST2- and IL-33-deficient mice showed defective Th2 activation and nasal eosinophilia to acute, but not chronic, ragweed exposure. TSLPR and ST2 double-deficient mice showed defective Th2 activation and nasal eosinophilia even after chronic ragweed exposure. These results demonstrate that TSLPR signaling is critical for the early phase response of AR by controlling the IgE-mast-cell/basophil pathway. The IL-33/ST2 pathway is central to nasal Th2 activation during acute allergen exposure, but both TSLPR and ST2 contribute to Th2 responses in chronically allergen-exposed mice.

Epithelial cells form the first physiological barrier against invasion by pathogens and the infiltration of allergens. Tight junctions (TJ), a cell-cell junctional complex located on the apical side of epithelial cells, have a critical role in the maintenance of epithelial barrier function. Impaired TJ structures are observed in patients with asthma, atopic dermatitis and nasal allergy; therefore, the dysfunction of epithelial barriers might be involved in the initiation or progression of allergic diseases. Protease-containing allergens and environmental pollutants enhance paracellular transport in epithelial cells through disruption of epithelial barrier function. This suggests that the disruption of TJ leads to the promotion of allergen delivery into the subepithelia, resulting in the progression of allergic diseases. Thus, protection of the epithelial barrier function might prevent or inhibit the development or exacerbation of allergic diseases. Recently, we reported that diesel exhaust particles (DEP), the main component of particulate patter 2.5, exacerbated allergic rhinitis (AR) in a mouse model through TJ disruption. In addition, we revealed that the oxidative stress-mediated pathway is involved in the effects caused by DEP and that nasal treatment with a reactive oxygen species (ROS) scavenger suppressed DEP-induced TJ disruption and exacerbation of AR. In this review, we focus on the relationship between TJ disruption and allergic disease. Furthermore, we discuss our recent findings regarding TJ disruption and the exacerbation of AR.

Human cystatin SN suppresses AR symptoms through inhibiting allergen protease activities and protecting the nasal TJ barrier in an allergen-specific manner. We propose that upregulation of nasal endogenous protease inhibitors, including cystatin SN, is a novel therapeutic strategy for protease allergen-induced AR.