Human colostrum and serum contain antibodies reactive to the intimin-binding region of the enteropathogenic Escherichia coli translocated intimin receptor

Background: In Brazil, enteropathogenic Escherichia coli (EPEC) diarrhoea i s endemic in young infants. A characteristic feature of EPEC adhesion to ho st cells is intimate attachment leading to the formation of distinctive "at taching and effacing" (A/E) lesions on mammalian cells. Two genes directly involved in intimate adhesion, ene and tir, encode the adhesion molecule in timin and its translocated receptor Tir, respectively. The intimin-binding domain of Tir was recently mapped to the middle part of the polypeptide (Ti r-M), and the amino (Tir-N) and carboxy (Tir-C) termini were found to be lo cated within infected host cells. Recently, it was shown that colostrum sam ples from mothers living in Sao Paulo contain IgA-class antibodies reactive with a number of proteins associated with EPEC virulence. It has also been shown that patients infected with verocytotoxin-producing E. coli O157 can produce antibodies to Tir. In the current study antibody responses to the different Tir domains were analyzed in sera and colostrum samples collected in an EPEC-endemic area of Brazil. Methods: Recombinant Tir, Tir-N, Tir-M, and Tir-C were expressed as His-tag ged protein in E. coli BL21a and purified on nickel columns. Western blot a nalysis was used to investigate colostrum IgA- and serum IgG-class antibodi es reactive with the Tir fragments. Results: Anti-Tir IgG antibodies were detected in the serum of children, wi th (63%) or without (50%) diarrhoea, Anti-Tir IgA-class antibodies were det ected in all the colostrum pools tested. With the use of both serum IgG- an d colostrum IgA-class antibodies, an immunodominant domain of the Tir-polyp eptide, Tir M, was identified. Conclusion: The intimin-binding region of Tir (Tir-M) is the immunodominant region of the polypeptide in humans. Both serum IgG-class and colostrum Ig A-class antibodies reacted predominantly with the Tir-M domain. (C) 2000 Li ppincott Williams & Wilkins, Inc.