K88 adhesins of enterotoxigenic Escherichia coli and their porcine enterocyte receptors

The three antigenic variants of the K88 fimbrial adhesin (K88ab, K88ac, and K88ad) of enterotoxigenic Escherichia coli (ETEC) each exhibit unique spec ificity with regard to their hemagglutination characteristics. The variants are also unique in the specificity of their binding to the brush borders o f enterocytes isolated from pigs with different genetic backgrounds, Divers ity in enterocyte binding specificity suggests the existence of several K88 receptors, expressed individually or in various combinations on porcine en terocytes. Three candidate receptors have been identified that may explain the adhesion of K88 fimbrial variants to various porcine enterocytes. These receptors are an intestinal mucin-type sialoglycoprotein (IMTGP), an intes tinal transferrin (GP74), and an intestinal neutral glycosphingolipid (IGLa d). The IMTGP binds K88ab and K88ac, but not K88ad, The GP74 binds K88ab, b ut not K88ac or K88ad, and the IGLad binds K88ad, but not K88ab or K88ac, E ach of the candidate receptors has been found in brush borders that are adh esive for the fimbriae that bind the respective receptor. They have not bee n found in brush borders that are not adhesive for those same fimbriae. The presence of IMTGP was highly correlated with susceptibility of neonatal gn otobiotic pigs to ETEC expressing K88ab or K88ac.