Bactericidal assay and passive protection studies of Leptospira interrogans

A previous investigation conducted in our laboratory resulted in the isolat ion of three putative outer surface proteins of 32, 40, and 45 kDa, which w ere expressed and conserved among six prevalent Leptospira interrogans sero vars. In this study, polyclonal antibodies were raised against whole cell a nd outer surface proteins isolated as detergent phase proteins (DPP) and ge l-purified proteins. These antibodies were subsequently used in an in vitro bactericidal assay and in passive immunization studies using cyclophospham ide-treated Balb/c mice. Bactericidal activity against the six serovars was found when anti-pomona whole cell serum and anti-pomona DPP serum were tes ted. Monospecific antisera to the 32 and 40 kDa antigens had bactericidal a ctivity on avirulent and virulent pomona serovar, but the titer was lower t han that of either DPP or whole cell antiserum. Cyclophosphamide-treated Ba lb/c mice injected with antibodies, generated against DPP or whole cell pom ona, were protected against challenge with 10(9) cells of serovar pomona st rain Pomona. Gel purified monospecific antisera to the 32 and 40 kDa protei ns protected only 67% of the mice. The efficiency of passive protection wit h those antibodies was demonstrated by prevention of multiplication and spr ead of Leptospira to the kidneys. Protection in cyclophosphamide-treated Ba lb/c mice was well correlated with bactericidal activity of antiserum in vi tro.