Allergenicity of recombinant troponin C from Tyrophagus putrescentiae

Background: The storage mite, Tyrophagus putrescentiae, produces potent allergens, many of which have not been characterized. This study was undertaken to characterize the allergenicity of troponin C from T. putrescentiae. Methods: A cDNA encoding 17.7 kDa troponin C, with homology to cockroach allergen Bla g 6, was identified from T. putrescentiae-expressed sequence tags. Recombinant troponin C was expressed and IgE responses to the recombinant protein were assessed in the presence and absence of 10 mM CaCl₂. Cross-reactivity between T. putrescentiae troponin C and Bla g 6 was tested using an inhibition ELISA. Results: Recombinant T. putrescentiae troponin C shares 62.7-85.5% homology with troponin C from various arthropods. Sera from 5 of 47 subjects in our study group (10.6%) showed IgE binding to the recombinant protein. Interestingly, addition of 10 mM CaCl₂ increased the intensity of IgE binding approximately 2-fold. In an immune-inhibition ELISA with these sera, T. putrescetiae troponin C and Bla g 6 did not cross-react significantly. Conclusions: Troponin C is a new mite allergen with calcium-dependent IgE reactivity.