The uniqueLegionella longbeachaecapsule favors intracellular replication and immune evasion

Abstract

AbstractLegionella longbeachaeandLegionella pneumophilacause Legionnaires’ disease despite species-specific differences in environmental niches, disease epidemiology, and genomic content. Here, we characterized a newL. longbeachaevirulence factor, a capsule that is expressed in post-exponential growth phase as shown by electron microscopy. Analysis of the capsule compositionviaHLPC revealed the presence of a highly anionic polysaccharide absent in a capsule mutant. The capsule is crucial for replication and virulencein vivoin a mouse model of infection and in the natural hostAcanthamoeba castellanii. It has anti-phagocytic function when encountering innate immune cells, it is involved in a low cytokine responses in mice and in human monocyte derived macrophages and helps to dampen the innate immune response. TheL. longbeachaecapsule is a novel virulence factor, unique among knownLegionellaspecies, that aidsL. longbeachaeto survive in specific niches and partly confersL. longbeachaeits unique infection characteristics.