HIGH-RESOLUTION MAPPING OF B-CELL EPITOPES WITHIN AN ANTIGENIC SEQUENCE FROM EIMERIA-TENELLA

Overlapping hexapeptides representing part of an Eimeria tenella antig enic sequence, shown to induce partial immunity to homologous challeng e in chickens, were synthesized on polypropylene pins (Pepskan techniq ue; Cambridge Research Biochemicals, Cambridge, United Kingdom). The b inding to these hexapeptides of antibodies from chickens infected and rabbits immunized with five species of Eimeria was studied, using the coated pins as the solid phase of an enzyme-linked immunoassay. Antibo dy binding to most regions of the sequence was demonstrated, with peak areas of antigenicity correlating with the most hydrophilic regions. A particularly hydrophilic and antigenic area towards the N terminus o f the sequence consists of a peptide motif repeated five times in the native antigen. Homologous antisera (chicken and rabbit anti-E. tenell a antisera) differed in their pattern of reactivity from heterologous sera raised against other Eimeria species. While the former bound to f ewer of the hexapeptides than the latter, they did so very strongly, i ndicating affinity maturation of the antibody response to E. tenella-s pecific sequences. No antibody reactivity to two regions of the sequen ce was detected. These regions occur in relatively hydrophilic areas a nd so are unlikely to be situated in transmembrane domains or in the i nterior of globular proteins. Synthetic peptides, as used in these exp eriments, make possible analysis of the fine specificity of immune res ponses and thus have a role to play in the development of novel vaccin es for the control of coccidiosis.