Two sequential layers of antibody‐mediated control of Legionella pneumophila infection

Abstract

Protective immunity against intracellular pathogens, including bacteria, usually relies on cellular immunity. However, antibodies are also implicated in mediating protection against intracellular bacteria. In case of airway infection with Legionella pneumophila (Lpn), the causative agent of Legionnaires' disease, pre-existing Lpn-specific antibodies were shown to afford protection within two days of infection. Here we dissected the early kinetics of Ab-mediated protection against airway Lpn infection and observed two kinetically and mechanistically distinct phases of protection by passively administered antibodies. Within the first hour of infection, Lpn-opsonizing antibodies provided almost 10-fold protection in an antibody Fc-dependent, but FcR-independent manner. Later on, by two days post infection, Lpn-specific Ab-mediated protection strictly involved FcγR, Syk kinase activity in alveolar macrophages and induction of reactive oxygen species (ROS). The findings presented here contribute to the understanding of the mechanisms of Ab-mediated control of Lpn infection in actively or passively immunized individuals.Keywords: alveolar macrophages r antibodies r IgG r pulmonary infection r Legionnaires' disease Additional supporting information may be found online in the Supporting Information section at the end of the article.

CD8+ T Cells Directed Against a Peptide Epitope Derived From Peptidoglycan-Associated Lipoprotein of Legionella pneumophila Confer Disease Protection

“…Moreover, alveolar macrophages were suggested to be an effector cell acting to inhibit bacterial multiplication ( 11 ). In animal models, antibodies were also associated with protection during early stages of airway infection ( 12 ). Similarly, immunization with L. pneumophila membranes resulted in induction of strong cellular immune responses and protective immunity against a lethal challenge with L. pneumophila ( 13 ).…”