Identification and characterization of OmpA-like proteins as novel vaccine candidates for Leptospirosis.

Leptospira is an important infectious Gram-negative bacterium causing Leptospirosis in mammals. Outer membrane proteins (OMPs) are key molecules in the interface between the cell and its environment. A group of putative leptospiral outer membrane proteins with an OmpA-like domain, comprising Lp0056, Lp0222, Lp3615, Lp3685, Lp4337 and Lbp328, were identified by bioinformatic methods and expressed as GST-tag fusion proteins. All these recombinant proteins were screened for immune-protective potential in hamsters challenged with Leptospira interrogans serovar Pomona. Out of these six proteins, three fusion proteins including Lp4337, Lp3685 and Lp0222 were found to be protective on the basis of survival. The immune response generated against these three recombinant proteins was evaluated on the basis of antibody production, lymphocyte proliferation and cytokine profiles in response to recall antigens whereas protective efficacy was assessed on the basis of survival and histopathological lesions in the vital organs (kidney, liver, and lung). Our results show that all three recombinant proteins generated strong immune responses, enhanced survival and reduced the severity of histopathological lesions. Of the proteins studied, Lp4337 generated the strongest immune response and was able to impart maximum protection (75%), followed by Lp3685 (58%), whereas Lp0222 generated lowest immune response correlating to protection (42%) against lethal infection of leptospira in the immunized animals. In contrast, control animals injected with PBS demonstrated low survival and had significant lesions. All these results clearly indicate that these three OmpA-like proteins may serve as novel vaccine candidates for leptospirosis.