Effect of structural stability on endolysosomal degradation and T-cell reactivity of major shrimp allergen tropomyosin

BackgroundTropomyosins are highly conserved proteins, an attribute that forms the molecular basis for their IgE antibody cross-reactivity. Despite structural similarities, their allergenicity varies greatly between ingested and inhaled invertebrate sources. In this study, we investigated the relationship between the structural stability of different tropomyosins, their endolysosomal degradation patterns and T-cell reactivity.MethodsWe investigated the differences between four tropomyosins - the major shrimp allergen Pen m 1 and the minor allergens Der p 10 (dust mite), Bla g 7 (cockroach) and Ani s 3 (fish parasite) - in terms of IgE binding, structural stability, endolysosomal degradation and subsequent peptide generation, and T-cell cross-reactivity in a BALB/c murine model.ResultsDespite their conserved primary structure and consequent IgE co-reactivity, the invertebrate tropomyosins displayed different protein stabilities. Pen m 1 and Ani s 3, but not Der p 10 and Bla g 7 elicited differential melting temperatures that were pH-dependent. Endolysosomal experiments demonstrated differential degradation, as a function of stability, generating different peptide repertoires. Pen m 1 T-cell clones, with specificity for sequences highly conserved in all four tropomyosins, did not proliferate with Der p 10, Bla g 7 and Ani s 3, indicating that these peptides were not naturally produced for other invertebrate tropomyosins.ConclusionsOur data suggest that, although invertebrate tropomyosins exhibit a high degree of IgE cross-reactivity due to conserved B-cell epitopes, they do not necessarily share identical cross-reactive T-cell epitopes. This is likely due to differential endolysosomal processing as a function of different structural stabilities.