The Blomia tropicalis allergen Blo t 7 stimulates innate immune signalling pathways through TLR2

BACKGROUND

Although the house dust mite species Blomia tropicalis is a leading cause of allergic diseases in tropical and subtropical regions, the identification and characterization of the allergenic proteins remain incomplete.

OBJECTIVE

We aimed to characterize a recombinant form of Blo t 7 (rBlo t 7) in terms of IgE reactivity, lipid-binding activity and ability to stimulate innate immunity.

METHODS

The mature Blo t 7 cDNA was cloned by PCR methods for the expression of a secreted form of the allergen in P. pastoris. The IgE reactivity to purified rBlo t 7 as well as the potential cross-reactivity with Der p 7 was determined by ELISA. The lipid-binding capacity of rBlo t 7 was assayed using fluorescent lipid probes. The stimulation of TLR2 signalling pathway by rBlo t 7 was examined in cell activation and reporter assays.

RESULTS

The amplified mature Blo t 7 cDNA revealed the presence of a 60 base pair insertion compared with the reference sequence registered in the GenBank database. Multiple protein sequence alignments of group 7 mite allergens confirmed that this longer deduced amino acid sequence was the authentic Blo t 7 polypeptide chain. Analysis of IgE reactivity can classify rBlo t 7 as an intermediate B. tropicalis allergen which displayed weak cross-reactivity with Der p 7. Purified rBlo t 7 was shown to bind selectively the naturally fluorescent lipid probe cis-parinaric (cPNA) with a dissociation constant of 2 μmol/L. The group 7 Blomia allergen stimulated the TLR2-, NF-kB- and MAPK-dependent production of IL-8 and GM-CSF in respiratory epithelial cells.

CONCLUSIONS & CLINICAL RELEVANCE

Through its propensity to transport fatty acids/lipids and to stimulate TLR2 signalling pathways in airway epithelial cells, Blo t 7 can represent a key allergen for the initiation of the B. tropicalis-induced airway inflammation.

Structural and IgE binding analyses of recombinant Der p 2 expressed from the hosts Escherichia coli and Pichia pastoris

BACKGROUND

The house dust mite allergen Der p 2 is one of the most important indoor allergens associated with allergic disease. Recombinant Der (rDer) p 2 with high IgE binding activity can be readily produced in Escherichia coli and Pichia pastoris, but the structure and IgE binding of the different methods of preparation have not been compared.

METHODS

Secondary structure was assessed by circular dichroism (CD). Intrinsic fluorescence and hydrophobic probe (1-anilinonaphthalene 8-sulphonic acid, ANS) were used to study the Der p 2 hydrophobic cavity. IgE binding was assessed by ELISA inhibition.

RESULTS

CD analysis showed the expected secondary structure for both nDer p 2 and refolded Der p 2 prepared from E. coli inclusion bodies but primarily random structure for Der p 2 secreted from P. pastoris. The secreted product, however, had disulphide bonding and could be refolded to a similar structure to natural Der (nDer) p 2 after precipitation with trichloro-acetic or ammonium sulphate. ANS binding and intrinsic Trp92 fluorescence showed that all recombinant proteins were different to nDer p 2 and that the allergen secreted from P. pastoris did not form a hydrophobic cavity. Despite the marked structural changes, all preparations of Der p 2 had similar IgE binding to nDer p 2.

CONCLUSION

Despite almost identical IgE binding, rDer p 2 prepared from both E. coli and P. pastoris showed structural differences to nDer p 2. Der p 2 secreted from P. pastoris lacked most of the natural structure, but refolding could induce the natural structure.

Genetic polymorphisms of major house dust mite allergens

BACKGROUND

Polymorphic sequence substitutions in the major mite allergens can markedly affect immunoglobulin E binding and T cell responses, but there are few studies on environmental isolates from Dermatophagoides pteronyssinus and none for D. farinae.

OBJECTIVE

To determine the sequence variation of the group 1 and 2 allergens from environmental D. pteronyssinus and D. farinae.

METHODS

RNA from each species was isolated from homes in Bangkok and the sequence of Der p 1, Der p 2, Der f 1, and Der f 2 determined from cDNA produced by high fidelity polymerase chain reactions.

RESULTS

The enlarged data set revealed preferred amino acid substitutions in residues 19, 81, and 215 of Der p 1 as well as sporadic changes. Der p 2 showed frequent variations with clusters of amino acid substitutions, but the canonical Der p 2.0101 was not found in any of 17 sequences. Der f 2 showed variants with clusters of substitutions similar to Der p 2 but in different amino acid positions and without any structural concordance. Der f 1 in contrast to the other allergens had few amino acid sequence substitutions.

CONCLUSIONS

The sequence information on variants provides data important for the optimal design of allergen formulations and useful for the genetic engineering and structure-function analyses of the major allergens.

Partial mattress encasing significantly reduces house dust mite antigen on bed sheet surface: a controlled trial

BACKGROUND

The most effective measure in house dust mite antigen reduction is mattress encasing with an impermeable membrane. A reduction in encasing costs will help increase patients' compliance in mite antigen avoidance.

OBJECTIVE

To investigate the effectiveness of partial mattress encasing with a nylon sheet produced in Thailand on the reduction of group I mite antigens from beddings.

METHODS

Sixty regularly-used beds from the house officers' dormitory of the Siriraj Hospital Mahidol University, Thailand, were randomly matched into two groups according to mite antigen levels. The control group (CG) used only regular cotton bed sheets whereas the partial encasing group (PG) used mattresses partially covered with a locally produced nylon sheet underneath the regular cotton bed sheets. Dust collection from the beddings was performed at baseline, 2, 4 and 6 months after application of the nylon sheet. Mite antigen levels were detected by a two step monoclonal antibody ELISA.

RESULTS

Mite antigen levels in both groups were not different at the beginning of the study. The PG had significantly lower group I antigen levels on regular bed sheet surfaces than the CG (P < .004) at the 2, 4 and 6 month timepoints. However, antigen levels on the mattress surface of the PG was significantly higher than the CG at the end of the study (P < .004). The barrier efficacy of the nylon sheet in preventing migration of group I mite antigens from the mattress to the surface of the regular cotton bed sheet was 94% whereas that of the regular cotton bed sheet was 66% (P = .007).

CONCLUSION

Partial mattress encasing with a locally made nylon sheet can reduce mite antigens on the regular cotton bed sheet surfaces for up to 6 months.

Complete mattress encasing is not superior to partial encasing in the reduction of mite allergen

BACKGROUND

Partial mattress encasing was found to be effective in reducing exposure to mite allergen in our previous investigation. We aimed to compare the short-term efficacy of partial and complete mattress encasing and to study mite-allergen levels within these mattresses.

METHODS

Thirty-one mattresses with high mite-allergen content were selected and were randomized into one of three study groups (10 for the control group [CG], 11 for the partial encasing group [PE], and 10 for the complete encasing group [CE]). A special mite-impermeable membrane was used. In the PE group, mattresses were encased on tops and sides only, whereas complete mattress encasement was undertaken in the CE group. Regular bedsheets were applied to all groups. Dust samples were collected over bedsheets at baseline and at months 3 and 6, and over mattresses at baseline and at the end of the study. Group I mite allergens in these samples were measured and compared.

RESULTS

At baseline, mattress mite allergens were similar in all groups (P=0.84). Mite allergen at the surfaces of bedsheets (over membranes) from both encasing groups were significantly reduced as compared to the CG group (P=0.003). Such reduction was maintained throughout the 6-month study. At the end of the study, mite antigens within mattresses in the CG and CE groups were increased as compared to baselines, whereas a decrease was observed in the PE group. Significant difference was observed only between the CG and PE groups (P=0.006).

CONCLUSIONS

Mattress encasing with a special membrane in this study was highly efficacious in the reduction of mite allergen (>90%). However, with complete encasing, mite allergens within mattresses were increased at the end of the study. Complete mattress encasing in a tropical environment does not offer any advantage over partial encasing.

House dust mite fauna in Thailand

House dust mites have been shown to be the most important source of allergen in Thailand. The results of our initial mite survey were in conflict with previous data reported 20 years ago. To evaluate the current condition of mite fauna in Thailand, we conducted a larger scale survey of house dust mites in dusts from three different parts of the country. A total of 630 mattress dust samples was collected from various types of housing from central, northern and northeastern parts of Thailand. House dust mites were identified and enumerated by standard techniques and 388 dust samples were analysed further for group I antigen by a two-site monoclonal antibody enzyme-linked immunosorbent assay. House dust mites were identified in 555/630 (88.1%) of dust samples collected; 27.6% of these 555 samples contained over 100 mites per gram of fine dust. Dermatophagoides pteronyssinus was the most abundant species found with a mean count of 87.2 mites per gram of dust (range 1-1460). Group I antigen was detected in 380/388 (97.9%) samples analysed and 330 of which (86.8%) contained over 2 micrograms/gm of group I antigen. The highest density of mites was found in dusts from northern Thailand whereas dusts with highest amount of antigen were those collected from the northeastern part. Some degree of correlation between mite count and mite allergen was observed (r2 = 0.133, P < 0.001). No significant difference in the mite count and mite allergen was found among various types of housings. House dust mites are the source of allergens ubiquitously found all over Thailand.(ABSTRACT TRUNCATED AT 250 WORDS)