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 devel oping countries that may be associated with chronic undernourishment, Breas t-feeding is effective in protecting infants against diarrhea and other inf ectious diseases. The aim of the study is to verify the ability of human co lostrum to inhibit aggregative adhesion of EAEC to HEp-2 cells and the pres ence of antibodies reactive to antigenic fractions of EAEC in colostrum sam ples. Methods. Enzyme-linked immunosorbent assay, immunoblotting and adhesion ass ays of EAEC to HEp-2 cells were done with pooled or individual colostrum sa mples (n = 35), Assays were performed with a well-known EAEC strain, 044:H1 8 E, coli (strain 042), Colostral IgA was isolated by affinity chromatograp hy 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-kD a band, compatible with the subunits of aggregative adherence fimbrial adhe sin II, characteristic of the 042 strain, absent in its plasmid-cured isoge nic strain, that was used as control. Individual colostrum samples also inh ibited adhesion, showed variable antibody titles against EAEC antigens in e nzyme-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 a dhesion of EAEC to HEp-2 cells and suggest that colostrum IgA antibodies re active to EAEC antigens may play a role in protection of infants against di arrhea caused by these bacteria.