Factors influencing the reactivity of Legionella antigens in immunofluorescence tests

We examined several factors for their effects on the serological reactivity of Legionella antigens used for direct or indirect fluorescent-antibody tests. These factors included media, methods of killing, strain differences, and the nature of the reactivity with diverse human sera. The maximum serological reactivities were obtained with charcoal-yeast extract agar; the relative antigenicity of cells grown on a chemically defined medium could be fourfold less than those grown on the charcoal-yeast extract agar. Cells grown at 25 degrees C showed only small antigenic differences from those grown at 35 degrees C but had better morphological and staining characteristics. Cells killed by 1% Formalin or 37% Formalin vapors showed a 20% less relative antigenicity than those killed by heat, but their cell walls stained more clearly and they had fewer aberrations. As tested with several human sera, cells of Philadelphia 1 showed great variation in relative antigenicity with changes in media or methods of preparation; Bellingham 1 was quite stable under these same conditions. The data suggest that Bellingham 1 had serogroup 1-specific antigens, reactive with human sera, which were not present in Philadelphia 1.