A major IgE epitope of rainbow trout collagen alpha2 chain

Bovine collagen is allergenic and its major IgE epitope has already been identified. Fish collagen is also allergenic but shows no IgE cross-reactivity with bovine collagen, implying that it has specific IgE epitopes. Therefore, this study was initiated to elucidate IgE epitopes of rainbow trout collagen alpha2 chain. Five overlapping proteins (R1-5; 221 or 225 amino acids long with an offset of 205 amino acids) covering the entire sequence of the rainbow trout collagen alpha2 chain were expressed in Escherichia coli. Immunoblotting experiments using 10 patients' sera reacting to fish collagen revealed that the major IgE epitope is included in the R5 protein (region 821-1,041). Then, 26 overlapping peptides (20 or 21 amino acids long with an offset of 8 amino acids) encompassing the sequence of the R5 protein were chemically synthesized and examined for IgE-binding ability by fluorescence ELISA. Region 941-960 was found to be most IgE-reactive. When evaluated by inhibition ELISA, this region accounted for more than 50% of the IgE reactivity to the R5 protein. Moreover, the same region was found to be IgE-reactive in bastard halibut and zebrafish collagen alpha2 chains, but not in bovine collagen alpha2 chain. Our results strongly suggest that region 941-960 is a major common IgE epitope of fish collagen alpha2 chains.