Lipopolysaccharide of Legionella as adjuvant for intrinsic and extrinsic antigens.

Lipopolysaccharide (LPS) isolated from Legionella species was found to be a potent adjuvant. When Legionella LPS was injected into animals as aqueous mixture or oil emulsion with protein antigens, it potentiated humoral antibody titers to these antigens by four- to sixfold. The LPS also acted as an intrinsic adjuvant to induce delayed hypersensitivity to the cross-reacting protein antigens present in cells of Legionella species, providing a potentially useful means for detecting legionellosis by skin test. The adjuvanticity of Legionella LPS was comparable in potency to Mycobacterium tuberculosis H37Ra in Freund's complete adjuvant. However, Legionella LPS caused much less tissue inflammation and appeared to function differently in some aspects.