Human IgG-cross reactive sarcoplasmic peptides in the freshwater catfish Rita rita.

Abstract

The prevalence and magnitude of clinical allergy caused by crossreacting proteins and panallergens appears to be increasing and reflects an increase in allergen sensitization. Fish is reported to be one of the most common causes of food allergic reactions. In general, clinically manifested food allergy is regarded as IgE mediated. However, there are some cases (~ 10%) in which IgE can not be proved. The present investigation was undertaken to identify the IgG-cross-reactive sarcoplasmic peptides in the Indian freshwater catfish Rita rita and to study the effect of boiling/ processing on their immunoreactivity. The epaxial (white) muscle proteins were extracted in PBS under three different conditions, viz. 'raw' (or uncooked, UC), 'boiled' (or cooked, C) and 'cooked with spices' as a normal ethnic preparation (CS). The protein profiles were analyzed by SDS PAGE and 2-D PAGE. Titer of human IgG-crossreactive sarcoplasmic peptides was determined by ELISA and cross-reactive proteins/ peptides were identified by immunoblot. By silver staining the SDS-polyacrylamide gel, ~23 protein bands were visualized in the protein extract (UC). Four 'thermostable' or 'boiling resistant' bands, viz. 55, 45, 23, & 20 kDa, were observed of which, the 23 kDa (pI 5.5-5.9), followed by 45kDa (pI 5.1-5.5) were the major ones. Muscle protein-specific IgG titers in the human sera, from a randomly selected population (n = 18), that included both fish-eating and fish-non-eating individuals varied from 1/1000 to 1/8000. Variable numbers of immunoreactive proteins were observed with different sera samples on immunoblot. In 'C' and 'CS' samples also immunoreactive bands were seen. There are cross-reactive proteins among the fish sarcoplasmic peptides that are recognized by human IgG and some of them are 'boiling resistant' and retain the immunoreactivity even after boiling and complex processing reactions that might account, partly, for the non-IgE-mediated food allergy. We could identify a 41kDa boiling-resistant sarcoplasmic peptide (pI 5.9-6.6), which appears to be a major IgG-crossreactive peptide in the freshwater catfish Rita rita.