Citation:
Thomas WR. Blueprint for the House Dust Mite. Int Arch Allergy Immunol. 2018;175(3):121-5.
Keywords:
Abstract:
Why would you want to sequence the house dust mite genome? Randall et al. [1] help explain this in an analysis of their assembly of the genomic sequence of Dermatophagoides pteronyssinus. The assembly, also reported by Waldron et al. [2], in fact follows those for D. farinae[3] and the closely related Euroglyphus maynei[4], but for the first time attention is directed to the issues that are important for allergy research, going beyond being a tool for the verification of newly discovered allergens. The completeness of the coverage of a genome assembly is a critical starting point for all genomic projects so considerable attention is given to the sequencing metrics, which showed high indicators of success. The genome length of 52.5 Mb encoding a predicted 19,368 proteins was similar to that found for D. farinae (53.5 Mb) and scabies (56.2 Mb) [5], although somewhat different to the 70.7 Mb found for E. maynei, indicating that further resolution is required. Despite the gross morphological difference of E. maynei from the 2 Dermatophagoides species, the sequences of the allergens of E. maynei have shown only the same disparity from Dermatophagoides sp. as that found between D. farinae and D. pteronyssinus. Therefore, if the difference is confirmed by continued analysis, it would be of major evolutionary significance. As expounded by Rider et al. [4], the original appraisals of completeness of the genome assemblies of the Acari were low but these were based on evolutionary expectations for the presence of different types of genes found in other arthropods and in particular mainly in insects. Now that a number of diverse acarid genome assemblies have been obtained for comparison it has been possible to appreciate their consistency and their completeness.
The D. pteronyssinus genomic sequence was found to contain all of the sequences for allergens registered in the WHO/IUIS allergen nomenclature subcommittee database as well as the homologues of all of the sequences entered into the database for D. farinae except for the EF-hand calcium-binding protein Der f 17, for which there is no recorded molecular information. It was similarly left unassigned by Chan et al. [3] for D. farinae. The homologues include those of the newly described Der f 24-34 allergens that were mostly identified in proteomic screens in China and have yet to be assessed for their IgE binding by gravimetric estimates or by titrations compared to the serodominant group 1 and 2 allergens. The ability to make recombinant D. pteronyssinus homologues of these components from the information in the genome not only opens up these investigations to studies in the many more regions where people are substantively or almost exclusively sensitized by D. pteronyssinus, but also to the possibility that investigators in these regions are more interested in making authenticable assessments. The T-cell responses of house dust mite-allergic subjects from Europe and America made to peptides representing predicted epitopes of many of these proteins showed that they did not induce substantive T-cell responses compared to the responses induced by the high IgE-binding components authenticated earlier with quantitative analyses [6], so there are questions to be resolved especially on the size and consistency of the responses and possible environmental influences and cross-reactivities.