Antibodies induced by enterotoxigenic Escherichia coli (ETEC) adhesin major structural subunit and minor tip adhesin subunit equivalently inhibit bacteria adherence in vitro

Abstract

Antibodies that block the adherence of enterotoxigenic Escherichia coli (ETEC) to host intestinal epithelial cells are protective. Multiepitope-fusion-antigens (MEFAs) carrying epitopes of ETEC adhesin major subunits or tip minor subunits induced antibodies against ETEC adherence. Adherence inhibition effectiveness of antibodies induced by major subunit epitopes versus minor tip subunit epitopes, however, has not been comparatively characterized. In this study, we immunized mice with a major subunit MEFA or a tip MEFA, evaluated MEFA anti-adhesin immunogenicity, and examined induced-antibodies against bacteria in vitro adherence or in vivo colonization in mice. Mice subcutaneously immunized with major subunit MEFA CFA/I/II/IV or tip MEFA showed no adverse effects and developed strong antigen-specific antibody responses. Data showed that antibodies derived from two MEFAs were equally effective against adherence of the bacteria expressing CS1, CS2, CS3, CS4/CS6, CS5/CS6, or CS6 adhesin in vitro . Subsequently, we immunized mice with CFA/I fimbriae, major subunit CfaB, or minor tip adhesin subunit CfaE. We found that antibodies induced by CFA/I, CfaB and CfaE equally inhibited in vitro adherence of ETEC strain H10407. Furthermore, we immunized mice with CFA/I fimbriae, CfaB, or CfaE, and then challenged the mice with H10407. Data showed that although not significantly, fewer H10407 bacteria colonized the immunized mice. These results suggest that ETEC adhesin major subunit and minor tip subunit should be equally effective in inducing neutralizing anti-adhesin antibodies, and that major subunit CFA/I/II/IV MEFA or tip MEFA, perhaps combined with toxoid fusion 3xSTa N12S -mnLT R192G/L211A , can be used for development of broadly protective vaccines against ETEC diarrhea.

Immunogenicity Evaluation of Chimeric Subunit Vaccine Comprising Adhesion Coli Surface Antigens from Enterotoxigenic <b><i>Escherichia coli</i></b>

“…Also, the serum IgG antibody level was higher in the immunized animals compared to the nonimmunized group, indicating the humoral immunity induction. According to the previous study, subcutaneously immunized mice with these tip subunits alone developed IgG antibody responses to both adhesive subunits [Seo et al, 2019]. Also, there was no significant increase in IgA antibody secretion in comparison with control mice.…”

Vaccines against gastroenteritis, current progress and challenges

“…207,208 CFA/I/II/IV MEFA, an epitope-and structure-based recombinant protein carries neutralizing epitope of the seven most important ETEC adhesins (CFA/I, CS1-CS6), induced antibodies that inhibit adherence of ETEC expressing any of these seven adhesins. [209][210][211] Because they are thermostabile and importantly antigenic compatible, 3xSTa N12S -mnLT R192G/L211A and CFA/I/II/ IV MEFA can be combined and co-administered,- 212 leading to the production of a multivalent ETEC subunit vaccine, MecVax. When parenterally (intramuscularly, intradermally, subcutaneously)…”

Human Mucosal IgA Immune Responses against Enterotoxigenic Escherichia coli

“…Although more than 20 different ETEC colonization factors have so far been described, the types of ETEC most commonly found associated with childhood diarrhea tend to produce one or more of the seven different colonization factors—colonization factor antigen I (CFA/I) and coli surface antigen 1 (CS1), CS2, CS3, CS4, CS5, and CS6 [ 76 , 81 , 82 , 83 , 84 , 85 ]. Many colonization factors are heteromorphic, filamentous structures called pili or fimbriae, which are usually made up of more than 1000 copies of stalk-forming structural subunits and a single tip adhesin [ 10 , 86 , 87 , 88 ]. Both the structural subunit and the tip adhesin bind to specific targets on the surface of enterocytes.…”

“…For example, both CfaB (structural subunit) and CfaE (tip adhesin) that make up CFA/I bind to glycosphingolipids and glycoproteins on the epithelial cell surface in the small intestine ( Figure 2 d). Studies have also demonstrated that antibodies targeting CfaB and CfaE are able to affect fimbrial elasticity and inhibit adherence of CFA/I-producing bacteria in vitro, respectively, indicating that the colonization factors may be suitable targets for vaccine development [ 10 , 87 , 89 ]. It should also be noted that some colonization factor-specific antibodies may cross-react with other colonization factors [ 90 , 91 ].…”