A high molecular weight antigen in Legionnaires' disease bacterium: isolation and partial characterization.

We isolated a high molecular weight antigen of the Legionnaires' disease (LD) bacterium by column chromatography. The antigen was composed of 35% carbohydrate, 2.6% protein, 1.8% phospholipid, and 1% 2-keto-3-deoxyoctonate and was important in the host's antibody response because it inhibited the indirect immunofluorescent and microagglutination titers of convalescent sera from patients with Legionnaires' disease. The antigen also formed precipitin bands with seven of 10 convalescent sera from patients with Legionnaires' disease. We found chemical and biological evidence of endotoxinlike activity associated with the antigen. Cell sonicates and acid extracts of the LD bacterium gave multiple bands in immunodiffusion with human convalescent serum and rabbit antisera prepared against heat-killed LD bacteria. The antigenic structure of the LD bacterium therefore appears complex.