Mite allergens and asthma

Absence of continuous epitopes in the house dust mite major allergens Der p I from Dermatophagoides pteronyssinus and Der f I from Dermatophagoides farinae

BACKGROUND

The house dust mite has been shown to be an important source of domestic allergens associated with immediate hypersensitivities. The Group I mite allergens Der p I from Dermatophagoides pteronyssinus and Der f I from D. farinae display extensive amino acid sequence homology and have similarities with cysteine protease enzymes.

OBJECTIVE

The availability of the complete amino acid sequences for these allergens allowed us to search for the allergic determinants within these molecules. The aim of the present investigation was to identify any continuous IgE-binding epitopes within these amino acid sequences. We also sought to test the validity of previously reported Der p I peptide epitope sequences.

METHODS

In order to identify any continuous IgE epitopes, the amino acid sequences of Der p I and Der f I were synthesized as decapeptides overlapping in sequence and coupled to plastic pins. The specific IgE-binding capacity of these peptides was assayed using an enzyme-linked biotin-streptavidin procedure and sera from patients known to be sensitive to these allergens. Previously reported Der p I peptide epitopes were synthesized as free peptides and tested for their ability to inhibit specific IgE binding to allergen extract discs.

RESULTS

None of the pin-coupled Der p I or Der f I peptides was found by the continuous epitope mapping procedure to bind significantly to specific IgE in the sera of hypersensitive patients. The previously reported Der p I peptide epitopes did not inhibit specific IgE binding to mite extract discs.

CONCLUSION

The specific IgE binding epitopes of the house dust mite allergens Der p I and Der f I are discontinuous in nature.

Comparative IgE responses to extracts of five species of house dust mite, using western blotting

IgE responses towards extracts of Dermatophagoides pteronyssinus, D. farinae, D. microceras, Euroglyphus maynei and Gymnoglyphus longior have been evaluated with sera from a mite sensitive population and the international reference pool of sera, NIBSC 82/528, using Western blotting. Using mite body and faecal extracts 21 of 29 mite protein bands responded to by sera were common to all five species of mite. All sera were unique with respect to proteins bound and species recognized. Mite proteins bound by more than 40% of sera included the Group II and III main allergens and protein bands 14 (MW 40.4 kD) and 21 (MW 27.8 kD), all of which were found in every mite species studied. The Group I allergen, found in all species, was bound by 29.4% of sera. Similar response profiles between mite species suggest that human specific IgE may bind predominantly to crossreactive determinants on mite allergens.

Frequency of DPB1*0401 is significantly decreased in patients with allergic asthma in a mulatto population

Allergic asthma (AA) is a multifactorial disease in which the IgE hyperresponsiveness to mite allergens is determinant for its pathogenesis and clinical picture. We have reported previously that IgE responsiveness to mite allergens in AA patients is linked to HLA and possibly controlled by a dominant suppression (Is) gene of that region. The present population study was done to detect alleles involved in the genetic control of mite IgE response that accompanies AA, using polymerase chain reaction and oligonucleotide DNA typing of DP locus. Instead of finding any significant positive association with AA, in this study we found that the allele DPB1*0401 is present mainly in the nonallergic control population and strikingly absent in patients (p less than 0.008), suggesting that this gene could confer resistance to AA and other atopic diseases. Our results add more evidence regarding the existence of Is genes in the HLA region involved in the control of IgE immune response to environmental allergens. Furthermore, they suggest that genes of HLA are important genetic components involved in the etiology of AA.