House dust mite (HDM) allergens are important factors in the increasing prevalence of asthma. The lung epithelium forms a barrier that allergens must cross before they can cause sensitization. However, the mechanisms involved are unknown. Here we show that the cysteine proteinase allergen Der p 1 from fecal pellets of the HDM Dermatophagoides pteronyssinus causes disruption of intercellular tight junctions (TJs), which are the principal components of the epithelial paracellular permeability barrier. In confluent airway epithelial cells, Der p 1 led to cleavage of the TJ adhesion protein occludin. Cleavage was attenuated by antipain, but not by inhibitors of serine, aspartic, or matrix metalloproteinases. Putative Der p 1 cleavage sites were found in peptides from an extracellular domain of occludin and in the TJ adhesion protein claudin-1. TJ breakdown nonspecifically increased epithelial permeability, allowing Der p 1 to cross the epithelial barrier. Thus, transepithelial movement of Der p 1 to dendritic antigen-presenting cells via the paracellular pathway may be promoted by the allergen’s own proteolytic activity. These results suggest that opening of TJs by environmental proteinases may be the initial step in the development of asthma to a variety of allergens.

Although prostaglandin D₂ is the most abundant prostanoid generated by human lung mast cells and causes bronchoconstriction in animals, its effects have not been studied in human beings. We have compared the effects of inhaled prostaglandin D₂ and prostaglandin F_2α on specific airway conductance in seven normal subjects and seven patients with mild allergic asthma. In dose–response studies in normal subjects, prostaglandin D₂ caused a significant (20±6 per cent) fall in specific airway conductance after the two highest concentrations (250 and 500 μg per milliliter), whereas prostaglandin F_2α had no effect. In the asthmatic subjects, both prostaglandin D₂ and prostaglandin F_2α caused a dose-related fall in specific airway conductance, starting at the lowest concentration of 4 μg per milliliter. Prostaglandin D₂ was 3.5 times more potent than prostaglandin F_2α. In a single-dose study of both drugs (250 μg per milliliter), a minor fall in specific airway conductance occurred with prostaglandin D₂ in the normal subjects, and a larger fall occurred with both drugs in the asthmatic subjects. Maximum effects were seen at three minutes: there was a 75±5 per cent fall with prostaglandin D₂ and a 33±8 per cent fall with prostaglandin F_2α. These results suggest that prostaglandin D₂ may be involved in the pathogenesis of bronchoconstriction in allergic asthma. (N Engl J Med 1984; 311:209–13.)

Sequence analyses have revealed the existence of homology between certain aeroallergens and proteolytic enzymes. This homology can be expressed functionally, but its significance to airway pathophysiology is unknown. Studies with Madin-Darby canine kidney cells and canine tracheal epithelial cells grown on plastic substrata or matrix proteins suggest that Der p1, a major allergen from the house dust mite Dermatophagoides pteronyssinus and a cysteine proteinase, or the unfractionated growth medium extract (SGME) from which it was purified, are both capable of causing cell detachment. The ability of both agents to produce functional changes in the barrier function of the epithelium was further demonstrated using isolated bovine airway preparations. Over a 3-h duration, both Der p1 and SGME elicited significant increases in the permeability of isolated sheets of bronchial mucosa to serum albumin. Exposure of isolated bronchial segments to luminally applied solutions of Der p1 resulted in histologic evidence of epithelial injury. Neither Der p1 nor SGME was active in these experimental systems unless chemically reduced, suggesting that the effect was initiated by cysteine proteinase activity. Similar augmentation of mucosal permeability and tissue injury was produced by bovine trypsin and collagenase from Clostridium histolyticum. In both the isolated mucosal sheet model and in cultured cells, the actions of Der p1 or SGME were associated with relatively little cytolysis, suggesting a specific action of the reagents on cell attachment. These results demonstrate a new functional activity of Der p1 that may be germane to the processes of allergen presentation, inflammatory cell activation, and chronic tissue injury.

Proteolytic digestion of human lung tissue dispersed a population of cells (HDLC) containing 1 to 8% mast cells but which were free from bronchial and vascular smooth muscle. Incubation of HDLC with anti-human IgE, which released a net 24.8 + 4.3% of mast cell-derived histamine, stimulated a 14-fold increase in the generation of PGD2, a seven-fold increase in TXB2, and less than a twofold increase in PGF2 alpha, immunoreactive PGE, (i-PGE) and 6-keto-PGF1 alpha. A similar profile of prostanoid release was observed when cells were challenged with epsilon-specific anti-IgE, indicating that the response was specific to the coupling of IgE Fc receptors. The calcium ionophore A23187 also released prostanoids from HDLC in approximately the same proportions as anti-IgE. This stimulus, however, released only 50% as much PGD2 per nanogram histamine than did IgE-dependent activation, thereby showing a fundamental difference in the mechanisms by which the two agents activate mast cells and liberate arachidonic acid for oxidative metabolism. In concentration-response and time course experiments, both secretory stimuli released prostanoids and histamine in parallel. After separation of lung cells by isopyknic centrifugation, challenge with anti-IgE or A23187 released PGD2 only from those fractions containing mast cells, the amount released corresponding closely to both the mast cell concentration and net histamine release. On pooling data from all experiments, the closest correlation was found between release of PGD2 and histamine when cells were stimulated with either anti-IgE (r = 0.813, p less than 0.001) or A23187 (r = 0.763, p less than 0.001), supporting a mast cell origin for PGD2. The release of other prostanoids in fractions not containing mast cells demonstrates that macrophages, monocytes, and lymphocytes have the capacity to generate TXB2, PGF2 alpha, and i-PGE both in the absence and presence of mast cells. Thus, although mast cells are likely to be the major source of PGD2 generated upon IgE-dependent stimulation of HDLC, other cells dispersed from lung tissue have the capacity to generate prostanoids directly after activation of their IgE-Fc receptors and, indirectly after the secretion of mast cell mediators.