Co-administration of rIpaB domain of Shigella with rGroEL of S. Typhi enhances the immune responses and protective efficacy against Shigella infection

Abstract

Shigella species cause severe bacillary dysentery in humans and are associated with high morbidity and mortality. The Invasion plasmid antigen (IpaB) protein, which is conserved across all Shigella spp., induces macrophage cell death and is required to invade host cells. The present study evaluates the immunogenicity and protective efficacy of the recombinant (r) domain region of IpaB (rIpaB) of S. flexneri. rIpaB was administered either alone or was co-administered with the rGroEL (heat shock protein 60) protein from S. Typhi as an adjuvant in a mouse model of intranasal immunization. The IpaB domain region (37 kDa) of S. flexneri was amplified from an invasion plasmid, cloned, expressed in BL21 Escherichia coli cells and purified. Immunization with the rIpaB domain alone stimulated both humoral and cell-mediated immune responses. Furthermore, robust antibody (IgG, IgA) and T-cell responses were induced when the rIpaB domain was co-administered with rGroEL. Antibody isotyping revealed higher IgG1 and IgG2a antibody titers and increased interferon-gamma (IFN-c) secretion in the co-administered group. Immunization of mice with the rIpaB domain alone protected 60%-70% of the mice from lethal infection by S. flexneri, S. boydii and S. sonnei, whereas co-administration with rGroEL increased the protective efficacy to 80%-85%. Organ burden and histopathological studies also revealed a significant reduction in lung infection in the co-immunized mice compared with mice immunized with the rIpaB domain alone. This study emphasizes that the co-administration of the rIpaB domain and rGroEL protein improves immune responses in mice and increases protective efficacy against Shigella infection. This is also the first report to evaluate the potential of the GroEL (Hsp 60) protein of S. Typhi as an adjuvant molecule, thereby overcoming the need for commercial adjuvants.

Intranasal Immunization of Mice with Multiepitope Chimeric Vaccine Candidate Based on Conserved Autotransporters SigA, Pic and Sap, Confers Protection against Shigella flexneri

“…A successful candidate vaccine against Shigella requires the induction of cell-mediated immunity, which plays an essential role in the elimination of these bacteria through the secretion of proinflammatory mediators from innate immune cells and increasing of CD8+ T cells-mediated cytotoxicity and cytokines secreted by CD4+ T cells inducing macrophages activation and the production of antibodies [ 27 , 31 ]. Moreover, the route of administration, the adjuvant and dose of vaccine are correlated with the vaccine effectiveness [ 29 ].…”

“…The protective efficacy of the candidate vaccine was evaluated in immunized groups (n = 5 mice/group) after 30 days of the last immunization. The lethal dose of S. flexneri 2457T (1 × 10 7 colony forming units (CFU)/mouse) was determined by serial dilution, plating, and counting colonies [ 27 , 31 ]. Briefly, S. flexineri was grown in TSA with 0.05% Congo red at 37 °C, and then colonies were grown in TSB at 37 °C in agitation until an OD 600 = 1.…”

“…These proteins interact with toll-like receptors (TLR), such as TLR2 and TLR4, and they stimulate the innate immune response [ 23 ]. Thus, HSPs, like GroEL (HSP 60) protein of Salmonella Typhi [ 24 , 25 ], have been successfully used as antigens [ 26 ] and adjuvants in the development of vaccine candidates [ 27 ]. The adjuvant capacity of GroEL has been evaluated in a recombinant domain-GroEL fusion protein with the conserved virulence protein IpaB of Shigella [ 28 ].…”

Understanding GroEL and DnaK Stress Response Proteins as Antigens for Bacterial Diseases

“…Together, these results suggest that GroEL and DnaK may be suitable as antigen carriers that lead to induction of cell-mediated immunity through both the CD4+ and CD8+ lineages, making them a diverse and enticing vaccine adjuvant. Likewise, the humoral and cell-mediated effects of a Shigella vaccine were enhanced when rGroEL was included as an adjuvant [ 92 ]. The ability to enhance both humoral and cell-mediated immune responses is an attractive feature as some commercial vaccines are primarily known for only eliciting one of the two arms of the immune system.…”

“…Being proteins, HSP can also be fused to antigens directly to induce immunity. For example, when developing a Shigella subunit vaccine, Shigella rGroEL was fused to the antigen IpaB as immunogenicity of the vaccine was enhanced when the two proteins were administered together [ 92 , 93 ]. The resulting fusion vaccine displayed a strong Th1/Th2 immune response while also providing high levels of protection in mice whereas the unfused antigens had a weaker response [ 93 ].…”