Evaluation of different ways of presenting LipL32 to the immune system with the aim of developing a recombinant vaccine against leptospirosis.

Leptospirosis, caused by bacteria of the genus Leptospira, is a direct zoonosis with wide geographical distribution. The implications in terms of public health and the economical losses caused by leptospirosis justify the use of a vaccine against Leptospira in human or animal populations at risk. In this study, we used the external membrane protein LipL32 as a model antigen, as it is highly immunogenic. The LipL32 coding sequence was cloned into several expression vectors: (i) pTarget, to create a DNA vaccine; (ii) pUS973, pUS974, and pUS977 for expression in BCG (rBCG); and (iii) pAE, to express the recombinant protein in Escherichia coli, for a subunit vaccine. Mice were immunized with the various constructs, and the immune response was evaluated. The highest humoral immune response was elicited by the subunit vaccine (rLipL32). However, with rBCG, the titer was still rising at the end of the experiment. The serum of vaccinated animals was able to recognize LipL32 on the membrane of the Leptospira, detected by indirect immunofluorescence. A monoclonal antibody anti-LipL32 was shown to inhibit the growth of Leptospira in vitro, indicating potential protection induced by the LipL32 antigen.