Antigen detection in enteropathogenic Escherichia coli using secretory immunoglobulin A antibodies isolated from human breast milk

Enteropathogenic Escherichia coli (EPEC) produces a characteristic attachin g and effacing (A/E) lesion in the small intestines of infected children. T he immune response to EPEC infection remains poorly characterized. The mole cular targets that elicit protective immunity against EPEC disease are unkn own. In this study protein antigens from EPEC were identified using secreto ry immunoglobulin A (sIgA) antibodies isolated from milk from Mexican women by Western blot analysis, Purified sIgA antibodies, which inhibit the adhe rence of EPEC to cells, reacted to many EPEC proteins, the most prominent o f which were intimin (a 94-kDa outer membrane protein) and two unknown prot eins with apparent molecular masses of 80 and 70 kDa. A culture supernatant protein of 110 kDa also reacted strongly with the sIgA antibodies. The mol ecular size of this protein and its reactivity with specific anti-EspC anti serum suggest that it is EPEC-secreted protein C (EspC). These EPEC surface protein antigens were consistently recognized by all the different sIgA sa mples obtained from 15 women. Screening of clinical isolates of various O s erogroups from cases of severe infantile diarrhea revealed that all EPEC st rains able to produce the A/E lesion showed expression of intimin and the 8 0- and 70-kDa proteins. Such proteins reacted strongly with the purified sI gA pool. Moreover, nonvirulent E. coli strains were unable to generate a sI gA response. The immunogenic capacities of the 80- and 70-kDa proteins as v irulence antigens have not been previously reported. The strong sIgA respon se to intimin and the 80- and 70-kDa proteins obtained in this study indica tes that such antigens stimulate intestinal immune responses and may elicit protective immunity against EPEC disease.