Evaluation of Type III Secretion Apparatus Components as Subunit Vaccine Candidates Against Shigella and Salmonella Infection in Mice

Abstract

This study focuses on the assessment of the translocators of the type III secretion system (TTSS) as protective antigens against Shigella and Salmonella infections in mice. Mice were given intramuscular and intranasal subunit vaccines formulated using extracellular components of the TTSA and various adjuvants. In Experiment 2 purified MxiH (needle), IpaD (tip protein) and IpaB (tip-associated translocator protein) were targeted in Shigella immunizations and in immunizations using purified Salmonella homologues, PrgI (needle), SipD (tip protein), and SipB (tip-associated translocator protein). Intramuscular immunizations were formulated with Freund's adjuvant, Freund's Incomplete Adjuvant, and Monophosphoryl lipid A (MPL). Intranasal immunizations were formulated with cholera toxin (CT), MPL and MPL with chitosan. Experiment 3 focused on using the TTSS needle tip proteins as vaccine components. IpaB and IpaD were used with MPL and AH as antigens for Shigella intramuscular immunizations. SipB, the SipB/SicA complex, and a SipB fragment with SipD were used with MPL and AH in Salmonella intramuscular vaccines and with double mutant heat-labile toxin (dmLT) for intranasal vaccines. Mice receiving Shigella vaccines were challenged intranasally with Shigella strain 2457T. Mice given Salmonella vaccines were challenged ororgastrically with Salmonella strain SL1344. Mice were monitored for up to two weeks post challenge. Experiment 2 offers two possible vaccine insights. First, the proteins PrgI, SipD and SipB with MPL and AH may provide protection against Salmonella infection when administered intramuscularly. Second, MxiH, IpaD and IpaB may provide protection when administered intranasally with CT as the adjuvant. Findings for Experiment 3 offer further understanding by using tip proteins as vaccine components. IpaD and IpaB in combination with MPL and AH appear to validate that protection against shigellosis may be possible with an intramuscular vaccine. Furthermore, the Salmonella SipB-SicA complex and SipD administered intranasally with dmLT may provide protection against Salmonella infection.