Parenteral immunization with IpaB/IpaD protects mice against lethal pulmonary infection by Shigella

• IpaB and IpaD proteins from Shigella are protective antigens.
• Delivery of IpaB/IpaD intranasally with dmLT protects mice.
• Use of a parenteral route modifies immunogenicity but retains protection.
• IL-17 secretion correlates with protection.

Shigellosis is an important diarrheal disease, especially among children in the developing world. About 90 million infections with Shigella spp are estimated to appear each year. We previously demonstrated that the type III secretion apparatus (T3SA) proteins IpaB and IpaD are protective antigens when administered intranasally using the mouse lethal pulmonary model. To simplify vaccine administration, we tested the parenteral route for IpaB and IpaD with several adjuvants and compared the immune response and protective efficacy via the intranasal route. We found that the intramuscular administration generated a response consisting of similar levels of serum IgG, a lack of IgA response and higher IL-17 secretion. Therefore, while parenteral administration yielded a unique pattern of immune responses, it retained the ability to protect mice in a lethal pulmonary challenge against S. flexneri when both proteins were used. Our results show the feasibility of generating protective parenteral vaccines against Shigella spp.