House dust mite: a new player in intestinal inflammation?

Epithelial barrier function properties of the 16HBE14o- human bronchial epithelial cell culture model

The human bronchial epithelial cell line, 16HBE14o- (16HBE), is widely used as a model for respiratory epithelial diseases and barrier function. During differentiation, transepithelial electrical resistance (TER) increased to approximately 800 Ohms × cm², while ¹⁴C-d-mannitol flux rates (J_m) simultaneously decreased. Tight junctions (TJs) were shown by diffusion potential studies to be anion-selective with P_C1/P_Na = 1.9. Transepithelial leakiness could be induced by the phorbol ester, protein kinase C (PKC) activator, 12-O-tetradecanoylphorbol-13-acetate (TPA), and the proinflammatory cytokine, tumor necrosis factor-α (TNF-α). Basal barrier function could not be improved by the micronutrients, zinc, or quercetin. Of methodological significance, TER was observed to be more variable and to spontaneously, significantly decrease after initial barrier formation, whereas J_m did not significantly fluctuate or increase. Unlike the strong inverse relationship between TER and J_m during differentiation, differentiated cell layers manifested no relationship between TER and J_m. There was also much greater variability for TER values compared with J_m. Investigating the dependence of 16HBE TER on transcellular ion conductance, inhibition of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) chloride channel with GlyH-101 produced a large decrease in short-circuit current (I_sc) and a slight increase in TER, but no significant change in J_m. A strong temperature dependence was observed not only for I_sc, but also for TER. In summary, research utilizing 16HBE as a model in airway barrier function studies needs to be aware of the complexity of TER as a parameter of barrier function given the influence of CFTR-dependent transcellular conductance on TER.

Insights Into Mucosal Innate Immune Responses in House Dust Mite-Mediated Allergic Asthma

The prevalence of asthma has been rising steadily for several decades, and continues to be a major public health and global economic burden due to both direct and indirect costs. Asthma is defined as chronic heterogeneous inflammatory diseases characterized by airway obstruction, mucus production and bronchospasm. Different endotypes of asthma are being recognized based on the distinct pathophysiology, genetic predisposition, age, prognosis, and response to remedies. Mucosal innate response to environmental triggers such as pollen, cigarette smoke, fragrances, viral infection, and house dust mite (HDM) are now recognized to play an important role in allergic asthma. HDM are the most pervasive allergens that co-habitat with us, as they are ubiquitous in-house dusts, mattress and bedsheets, and feed on a diet of exfoliated human skin flakes. Dermatophagoides pteronyssinus, is one among several HDM identified up to date. During the last decade, extensive studies have been fundamental in elucidating the interactions between HDM allergens, the host immune systems and airways. Moreover, the paradigm in the field of HDM-mediated allergy has been shifted away from being solely a Th2-geared to a complex response orchestrated via extensive crosstalk between the epithelium, professional antigen presenting cells (APCs) and components of the adaptive immunity. In fact, HDM have several lessons to teach us about their allergenicity, the complex interactions that stimulate innate immunity in initiating and perpetuating the lung inflammation. Herein, we review main allergens of Dermatophagoides pteronyssinus and their interactions with immunological sentinels that promote allergic sensitization and activation of innate immunity, which is critical for the development of the Th2 biased adaptive immunity to HDM allergens and development of allergic asthma.

The Role of Dust Mites in Allergy

House dust mites are an unsurpassed cause of atopic sensitization and allergic illness throughout the world. The major allergenic dust mites Dermatophagoides pteronyssinus, Dermatophagoides farinae, Euroglyphus maynei, and Blomia tropicalis are eight-legged members of the Arachnid class. Their approximately 3-month lifespan comprises egg, larval, protonymph, tritonymph, and adult stages, with adults, about one fourth to one third of a millimeter in size, being at the threshold of visibility. The geographic and seasonal distributions of dust mites are determined by their need for adequate humidity, while their distribution within substrates is further determined by their avoidance of light. By contacting the epithelium of the eyes, nose, lower airways, skin, and gut, the allergen-containing particles of dust mites can induce sensitization and atopic symptoms in those organs. Various mite allergens, contained primarily in mite fecal particles but also in shed mite exoskeletons and decaying mite body fragments, have properties that include proteolytic activity, homology with the lipopolysaccharide-binding component of Toll-like receptor 4, homology with other invertebrate tropomyosins, and chitin-cleaving and chitin-binding activity. Mite proteases have direct epithelial effects including the breaching of tight junctions and the stimulation of protease-activated receptors, the latter inducing pruritus, epithelial dysfunction, and cytokine release. Other components, including chitin, unmethylated mite and bacterial DNA, and endotoxin, activate pattern recognition receptors of the innate immune system and act as adjuvants promoting sensitization to mite and other allergens. Clinical conditions resulting from mite sensitization and exposure include rhinitis, sinusitis, conjunctivitis, asthma, and atopic dermatitis. Systemic allergy symptoms can also occur from the ingestion of cross-reacting invertebrates, such as shrimp or snail, or from the accidental ingestion of mite-contaminated foods. Beyond their direct importance as a major allergen source, an understanding of dust mites leads to insights into the nature of atopy and of allergic sensitization in general.

Asthma Is Associated With Subsequent Development of Inflammatory Bowel Disease: A Population-based Case-Control Study

BACKGROUND & AIMS

Asthma and the inflammatory bowel diseases (IBD) each arise through complex interactions between genetic and environmental factors, and share many environmental risk factors. We examined the association between asthma and Crohn's disease or ulcerative colitis.

METHODS

We performed a population-based case-control study using health administrative data from the province of Alberta, Canada. The odds of a diagnosis of asthma preceding the diagnosis of either Crohn's disease (N = 3087) or ulcerative colitis (N = 2377) were compared with the odds of diagnosis of asthma among persons without IBD (N = 402,800) using logistic regression. Effect measure modification by age at diagnosis of IBD (16 years or less, 17-40 years, or older than 40 years) was tested using a likelihood ratio test.

RESULTS

A diagnosis of asthma was associated with increased odds of incident Crohn's disease (adjusted odds ratio [OR], 1.45; 95% confidence interval [CI], 1.31-1.60). No effect measure modification was observed for age at diagnosis for Crohn's disease (P = .42). However, we observed effect measure modification by age at diagnosis for ulcerative colitis (P = .0103), with an adjusted OR of 1.49 (95% CI, 1.08-2.07) among individuals diagnosed at an age of 16 years or less (OR) and an adjusted OR of 1.57 (95% CI, 1.31-1.89) among individuals diagnosed at an age older than 40 years. However, there was no association between asthma and ulcerative colitis among individuals diagnosed between ages 17 and 40 (adjusted OR, 1.05; 95% CI, 0.86-1.26).

CONCLUSIONS

In a population-based case-control study, we associated asthma with Crohn's disease, and with early and late-onset ulcerative colitis.