Escherichia coli K88ab fimbrial antigen (K88ab)

The Escherichia coli K88ab fimbrial antigen, also known as the F4ab adhesin, is a critical virulence factor found on the surface of enterotoxigenic Escherichia coli (ETEC) strains that primarily infect swine [1, 2]. These fimbriae are long, filamentous proteinaceous appendages composed of subunits, most notably the major subunit FaeG, which mediates the attachment of the bacteria to specific glycoprotein receptors on the brush border of porcine intestinal epithelial cells [2, 12]. This adhesion is the essential first step in the pathogenesis of neonatal and post-weaning diarrhea, allowing the bacteria to colonize the small intestine and deliver enterotoxins [1, 13]. Because of its pivotal role in infection, the K88ab antigen is a major target for the development of veterinary vaccines and passive immunization strategies [3, 7]. Therapeutic interventions, such as maternal vaccination or the administration of specific monoclonal antibodies, aim to block this adhesive interaction, thereby preventing colonization and the resulting clinical disease [5, 13]. The antigen exists in several variants (ab, ac, and ad), which presents a challenge for broad-spectrum vaccine efficacy due to immunological heterogeneity among the different serotypes [2, 15].

Other names

F4ab fimbrial adhesinK88ab antigenFaeG major subunitK88 pilinF4ab antigenK88 fimbrial protein AB

The primary mechanism of action involves the induction of neutralizing antibodies (IgA and IgG) or the use of competitive inhibitors to block the binding of the fimbrial adhesin to host intestinal receptors, thereby preventing bacterial colonization and subsequent enterotoxin-mediated diarrhea [1, 5, 13].