Clinical determinants and time course of serum antibody response against listeriolysin O in experimental listeriosis

The serum antibody response against listeriolysin O (LLO) was studied in goats experimentally infected with Listeria monocytogenes, using two sequential oral inoculations at 8 months interval. The serum IgG antibody response against LLO correlated closely with that against the whole bacterium, supporting the role of LLO as the major antigenic determinant of the humoral response against L. monocytogenes. However, only severe listeric infections were accompanied by a distinct anti-LLO antibody response, whereas milder, albeit bacteraemic infections remained only weakly responsive or totally non-responsive. Elevated anti-LLO IgG antibody levels persisted for several months after past infection and even high levels of anti-LLO IgG antibodies without evidence of past or ongoing listeriosis were found. Therefore, in the serodiagnosis of listeriosis, the determination of antiLLO antibody response may be applicable only in severe listeric infections and should always be based on IgG seroconversion.