Identification and characterization of epitopes on Cyn d I, the major allergen of Bermuda grass pollen.

Abstract

We identified three epitopes on Cyn d I by using four anti-Cyn d I monoclonal antibodies (MoAbs). In a cross-inhibition binding assay, the binding of MoAbs 1-61 and 10-7 to Cyn d I was completely blocked by each other but not by MoAbs 4-37 and 11-7; the binding of MoAb 4-37 and MoAb 11-7 to Cyn d I was inhibited by themselves but not by other MoAbs. The epitope recognized by MoAbs 1-61 and 10-7 is designated as E1, and those recognized by MoAbs 4-37 and 11-7 are designated as E2 and E3, respectively. In a radioallergosorbent inhibition assay, we found that MoAbs 1-61 and 4-37 (1:50 diluted) can inhibit the binding of human Immunoglobulin Es to Cyn d I by more than 30%, whereas MoAb 11-7 was less efficient (reduced by only 6%). These results suggest that both E1 and E2 are major allergenic epitopes but that E3 is only a minor one. Further characterization of E1 and E2 reveals that they are labile in alkaline but resistant to acid and sodium periodate treatments. Moreover, E1 is heat-labile, but guanidine- and urea-sensitive, whereas E2 is not. Both E1 and E2 lost their antigenicity after reduction and alkylation. Results of the present study provide important information on the physicochemical properties of major allergenic epitopes on Cyn d I, which may be useful for future development of therapeutic peptides for patients allergic to Bermuda grass pollen.