Shigella flexneri vaccine development: Oral administration of peptides derived from the 49.8 kDa pili protein subunit activates the intestinal immune response in mice

Background and Aim: The morbidity and mortality of Shigella infections remain a global challenge. Epitope-based vaccine
development is an emerging strategy to prevent bacterial invasion. This study aimed to identify the ability of the 49.8 kDa
pili subunit adhesin protein epitope of Shigella flexneri to induce an intestinal immune response in mice.
Materials and Methods: Thirty adult male Balb/c mice were divided into a control group, cholera toxin B subunit (CTB)
group, CTB+QSSTGTNSQSDLDS (pep_1) group, CTB+DTTITKAETKTVTKNQVVDTPVTTDAAK (pep_2) group,
and CTB+ ATLGATLNRLDFNVNNK (pep_3). We performed immunization by orally administering 50 µg of antigen and
50 µl of adjuvant once a week over 4 weeks. We assessed the cellular immune response by quantifying T helper 2 (Th2) and
Th17 using flow cytometry. In addition, we assessed the humoral immune response by quantifying interleukin (IL-4), IL-17,
secretory immunoglobulin A (sIgA), and β-defensin using enzyme-linked immunoassay. Statistical analysis was performed
using one-way analysis of variance and Kruskal–Wallis test.
Results: Peptide oral immunization increases the cellular immune response as reflected by the increase of Th2 (p=0.019) and
Th17 (p=0.004) cell counts, particularly in the CTB_pep_1 group. Humoral immune response activation was demonstrated
by increased IL-4 levels, especially in the CTB+pep_3 group (p=0.000). The IL-17 level was increased significantly in
the CTB+pep_1 group (p=0.042). The mucosal immune response was demonstrated by the sIgA levels increase in the
CTB+pep_3 group (p=0.042) and the β-defensin protein levels (p=0.000).
Conclusion: All selected peptides activated the cellular and humoral immune responses in the intestine of mice. Further
studies are necessary to optimize antigen delivery and evaluate whether the neutralizing properties of these peptides allow
them to prevent bacterial infection.