The polymeric stability of the Escherichia coli F4 (K88) fimbriae enhances its mucosal immunogenicity following oral immunization

Abstract

a b s t r a c tOnly a few vaccines are commercially available against intestinal infections since the induction of a protective intestinal immune response is difficult to achieve. For instance, oral administration of most proteins results in oral tolerance instead of an antigen-specific immune response. We have shown before that as a result of oral immunization of piglets with F4 fimbriae purified from pathogenic enterotoxigenic Escherichia coli (ETEC), the fimbriae bind to the F4 receptor (F4R) in the intestine and induce a protective F4-specific immune response. F4 fimbriae are very stable polymeric structures composed of some minor subunits and a major subunit FaeG that is also the fimbrial adhesin. In the present study, the mutagenesis experiments identified FaeG amino acids 97 (N to K) and 201 (I to V) as determinants for F4 polymeric stability. The interaction between the FaeG subunits in mutant F4 fimbriae is reduced but both mutant and wild type fimbriae behaved identically in F4R binding and showed equal stability in the gastro-intestinal lumen. Oral immunization experiments indicated that a higher degree of polymerisation of the fimbriae in the intestine was correlated with a better F4-specific mucosal immunogenicity. These data suggest that the mucosal immunogenicity of soluble virulence factors can be increased by the construction of stable polymeric structures and therefore help in the development of effective mucosal vaccines.

Immune responses elicited in mice with recombinant Lactococcus lactis expressing F4 fimbrial adhesin FaeG by oral immunization

“…Statistical analyses (SPSS 11.0) were performed using a General Linear Model (Repeated Measures Analysis of Variance) to assess F4-specific antibody levels and F4-specific ASC, adjusting for multiple comparisons by Bonferoni (Verdonck et al 2008). P value of less than 0.05 was considered statistically significant.…”

“…Significant difference (P<0.05) between low dose and high dose (a), between high dose and high dose + CTB (b). Black arrow: oral immunization 1999b; Verdonck et al 2008). F4 fimbrial adhesin FaeG has been expressed in several delivery vehicles such as non-enterotoxigenic E. coli (Verdonck et al 2004b;Yahong et al 2006), alfalfa (Joensuu et al 2006) and Salmonella typhimurium (Attridge et al 1997), but the immune efficacy of rFaeG with the use of these vectors was varied.…”

“…Once colonized, ETEC then causes metabolic disorder of enterocytes by production and delivery of heat-stable enterotoxins (ST) and/or heat-labile enterotoxins (LT), eventually leading to piglet diarrhea (Caloca and Suarez 2006). Since the adhesion of ETEC to the receptors is a primary and essential step of infection, the fimbrial adhesin protein is considered to be an important virulence factor of ETEC ( Van den Broeck et al 1999b;Verdonck et al 2008). However, the role of fimbriae in ETEC has not yet been sufficiently explored.…”

“…Therefore, weaned piglets need to acquire more effective immune protection. Since the intestinal surfaces of piglets are in direct contact with environmental pathogens and are the main invading portal for pathogenic bacteria, weaned piglets can be effectively protected by oral administration of F4 fimbriae or recombinant FaeG (rFaeG), which induces a local immune response at the mucosal surfaces and prevents ETEC from invading the body at the source of infection (Verdonck et al 2004b(Verdonck et al , 2008. Oral immunization is considered a more desirable approach against diarrhea in weaned piglets.…”

Subcutaneous or Oral Immunization of Mice with <i>Lactococcus lactis</i> Expressing F4 Fimbrial Adhesin FaeG

“…Consequently, ETEC produces enterotoxins and causes piglet diarrhea. The F4 fimbriae of ETEC are composed of a repeating major subunit, FaeG and some minor subunits [23]. Since FaeG has both adhesive and antigenic properties, the development of anti-adhesive vaccines to prevent ETEC infections has long been pursued by researchers [16,17,22].…”