Antigenic Homogeneity among Legionella pneumophila Serogroups 1 to 6 Evaluated by Crossed Immunoelectrophoresis

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Abstract
The objective of this study was to investigate the antigenic profiles of Legionella pneumophila serogroups 1 to 6 and antigenic relatedness among individual serogroups. A reference precipitate pattern which had 71 anodic- and 6 cathodic-migrating antigens was established with a pooled antigen preparation of sonicated L. pneumophila cells of serogroups 1 to 6 against purified homologous rabbit antibody. Sixteen antigens made heat stable by boiling for 10 min were found, of which one could be demonstrated as being the common antigen of gram-negative bacteria and another could be shown as being the serogroup-specific antigen of L. pneumophila. Precipitin patterns similar in overall appearance and precipitin numbers were demonstrated for each serogroup by testing antigen preparations of individual serogroups against reference system antibody. Crossed-line experiments revealed < 5 non-cross-reacting antigens among serogroups, with resulting matching coefficients (ratio of the number of cross-reactive to total antigens) all above 0.91. The matching coefficients found when testing antigen preparations from L. pneumophila serogroups 7 and 8 were 0.93 and 0.99, respectively. By contrast, thematching coefficients of Tatlockia micdadei, Fluoribacter bozemanae, Fluoribacter dumoffi, and Fluoribacter gormanii was 0.39, 0.45, 0.39, and 0.41, respectively. Comparison of precipitate patterns and experimental results between the previously described monovalent L. pneumophila serogroup 1 system and the polyvalent crossed immunoelectrophoresis system with L. pneumophila serogroups 1 to 6 substantiated the antigenic homogeneity of L. pneumophila and the significant difference in antigenic composition between this taxon and other members of the family Legionellacea. In addition, reproducibility of the antigenic profile of L. pneumophila by crossed immunoelectrophoresis was demonstrated.

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