It has long been recognized that the allergy to mites of the genus Dermatophagoides is associated with diseases such as asthma, rhinitis, and atopic dermatitis (1, 2). In this regard, the species D. pteronyssinus and D. farinae predominate and many studies have been performed to identify the allergens they produce. Studies on D. pteronyssinus have, for example, demonstrated that at least six major allergens are of clinical importance (3, 4). One of the major mite allergens, designated Derp l, has been purified and shown to react with anti-mite IgE antibodies in up to 80% of allergic sera (3-5). This allergen, reportedly a glycoprotein of mol wt 27 x 1Os , appears to be an excretory product associated with fecal particles (6).Currently, the diagnosis and immunotherapy of the house dust mite allergy is based on the use of crude mite preparations (7). Developments in this field have been hampered by the small or variable quantities of mite allergens present in the extracts . To help overcome these limitations, and to facilitate further studies, the molecular cloning of mite allergens is being investigated in our laboratory . To date, a cDNA clone coding for the allergen Der p 1 has been isolated and shown to contain a 0 .8-kb cDNA insert (8) . We now report the sequence analyses of the Der p 1 cDNA clone and the similarity between its inferred amino acid sequence and the group of cysteine proteases.

A cDNA clone coding for the major house dust mite allergen Der p 1 was isolated from a lambda gt 11 library. Its sequence correlates with known amino acid sequences of Der p 1 and it produces a fusion protein which reacts with rabbit anti-Der p 1 antiserum.

The acarofauna and Der p I allergen concentrations in dust samples from mattresses and lounge room carpets obtained from 20 homes from two coastal cities. Perth and Bunbury, were determined. All samples were shown to contain mites and the geometric mean numbers of total mites/g of mattress and carpet dust for Perth and Bunbury were 480 and 263, and 585 and 992, respectively. Carpets from both centres had a significantly (P less than 0.02) greater mean number of mite species (Perth 9.1, Bunbury 9.0) than mattresses (Perth 5.2, Bunbury 5.7). The predominant mite species were D. pteronyssinus, E. maynei and Tarsonemus spp. D. farinae was found to be absent from all dust samples examined. E. maynei was present in the 10 Bunbury homes and in 50% of the Perth homes, ranging from 0 to 81% of mites identified. The arithmetic mean Der p I concentrations in the mattresses and carpets in Perth and Bunbury were 4.2 and 4.1, and 3.8 and 9.2 micrograms/per gram of fine dust, respectively, and Der p I concentration correlated with mite counts (r = 0.75; P less than 0.001). The concentration of Der p I equivalent per 100 mites was 1.5 micrograms. The data are consistent with the view that asthmatic patients in Western Australia have significant exposure to a variety of house dust mites and that E. maynei may be clinically significant.

Summary The physicochemical and immunochemical characteristics of the allergens from Dermatophagoides pteroyssinus have been described, in particular those for the allergens designated Dpt 4 and Dpt 12. Dpt 4 is a high molecular weight allergen with an apparent molecular weight of 274,000 daltons and a pI of 4.5. In contrast, the antigenically unrelated Dpt 12 has an apparent molecular weight of 24,000 daltons and a pI 6.6. Both allergens demonstrate heterogeneity, either in molecular weight or pI. Dpt 12 appears to be the major allergen in extracts of D. pteronyssinus and probably corresponds to the low molecular weight allergen previously described by other workers.

Recent studies indicate that the majority of clinically important aeroallergens are biochemically active. A diverse range of properties have been demonstrated but most possess either enzymatic activity (principally hydrolytic), enzyme inhibitory activity, low molecular weight ligand transporting or regulatory properties. In addition, some allergens are glycosylated and/or are structurally similar to proteins which have evolved to function in the respiratory system per se. Little attention has been given to the possibility that the biochemical activity of an allergen or any post-translational modifications contribute to sensitization. In this review, mechanisms with the potential to influence immunogenicity are discussed including interaction with respiratory secretions, epithelial disruption, interactions with immunocompetent cells and receptor mediated endocytosis. Given that many aeroallergens are structurally and functionally similar to a variety of endogenous (e.g. lysosomal enzymes) and exogenous proteins (e.g. microbial enzymes and glycoproteins), particular attention has been directed to the latter. This process represents an important non-adaptive defence mechanism which has evolved to recognize and process such proteins and it is feasible that it plays a similar role in the processing of some allergens entering the respiratory system.