Leptospirosis is a zoonotic disease of global importance. The current killed vaccine provides serovar-specific protection without sterilizing immunity. Several surface antigens, including Leptospira immunoglobulin-like proteins (LigA and LigB), have been identified as subunit vaccine candidates; however, they require potent adjuvants. Bacterial Lipopolysaccharide (LPS), including lipid A, is a well-known immunostimulatory agent, and the formulation of Monophosphoryl Lipid A (MPLA) in Alum is a clinical adjuvant. Being less endotoxic, we tested the adjuvant activity of lipid A purified from L. interrogans serovar Pomona (PLA) for its ability to activate innate and enhance antigen-specific adaptive immune response. PLA-induced activation of macrophages similar to levels induced by MPLA, albeit at a much higher dose, indicating that it is less stimulatory than MPLA. Mice immunized with a Variable portion of LigA (LAV) formulated in Alum and PLA (LAV-Alum-PLA) induced significantly higher levels of LAV-specific humoral and cellular immune response than Alum but similar to levels induced by Alum-MPLA. The adjuvant activity of PLA seems to be quite similar to MPLA and primarily mediated through enhanced recruitment, activation, and uptake of antigens by innate immune cells. Moreover, like MPLA, the PLA formulation was able to generate a long-term memory response. Most importantly, PLA demonstrated better potency than MPLA formulation and generated sterilizing immunity against challenge in a hamster model of leptospirosis. Altogether, our study has provided important insight into the adjuvant activity of Leptospira lipid A and has opened avenues for the development of LPS-based vaccines against this dreadful zoonosis.

Schistosomiasis, a crippling ailment that afflicts over 220 million people worldwide. Yet or up till now, there is no vaccine for schistosomiasis, and chemotherapy relies heavily on a single drug, the praziquantel. The present study was undertaken to investigate the therapeutic effect of Monophosphoryl Lipid A (MPLA) as an adjuvant in soluble egg antigen (SEA) vaccinated mice against the deleterious pathological impacts induced in hepatic tissues of mice by Schistosoma mansoni infection. In addition, to study the associated parasitological, immunological and biochemical parameters. Parasitological parameters showed that intraperitoneal injection of MPLA into SEA-vaccinated and S. mansoni-infected mice was effective to a significant degree in reducing the worm and egg burden, granuloma count and diameter as well as the total area of infection in their livers versus SEA-untreated but infected ones. In addition, MPLA showed ameliorative action on the elevated liver oxidative stress marker, including malondialdehyde (MDA) and decrease in the level of the antioxidant enzymes, reduced glutathione (GSH) and catalase (CAT) which may have a role in the liver damage and fibrosis due to S. mansoni infection. In conclusion, treatment with MPLA has multi-functions in attenuating the deleterious impacts of S. mansoni infection in mice livers. Its effects are mediated through a reduction of ova count, worm burden, granuloma diameter and amelioration of antioxidant defense systems, and liver function biomarkers.