Inhibition of enteroaggregative Escherichia coli adhesion to HEp-2 cells by secretory immunoglobulin A from human colostrum

BACKGROUND.Enteroaggregative Escherichia coli (EAEC) is an important agent of the persistent diarrhea among low socioeconomic level children in developing countries that may be associated with chronic undernourishment. Breast-feeding is effective in protecting infants against diarrhea and other infectious diseases. The aim of the study is to verify the ability of human colostrum to inhibit aggregative adhesion of EAEC to HEp-2 cells and the presence of antibodies reactive to antigenic fractions of EAEC in colostrum samples. METHODS.Enzyme-linked immunosorbent assay, immunoblotting and adhesion assays of EAEC to HEp-2 cells were done with pooled or individual colostrum samples (n = 35). Assays were performed with a well-known EAEC strain, O44:H18 E. coli (strain 042). Colostral IgA was isolated by affinity chromatography in Sepharose anti-human alpha chain column. RESULTS.Total colostrum and isolated IgA inhibited EAEC adhesion, and this ability was associated with the presence of IgA antibodies against a 15-kDa band, compatible with the subunits of aggregative adherence fimbrial adhesin II, characteristic of the 042 strain, absent in its plasmid-cured isogenic strain, that was used as control. Individual colostrum samples also inhibited adhesion, showed variable antibody titles against EAEC antigens in enzyme-linked immunosorbent assay and recognized many antigenic fractions in immunoblotting assays, including the 15-kDa band. CONCLUSIONS.These results confirm that IgA from human colostrum inhibits adhesion of EAEC to HEp-2 cells and suggest that colostrum IgA antibodies reactive to EAEC antigens may play a role in protection of infants against diarrhea caused by these bacteria.