[Ultrastructural localization of type-specific antigen of legionella pneumophila]

Cell suspensions of Legionella pneumophila, a virulent Philadelphia I strain, were incubated with rabbit antiserum to type-specific heat-sensitive antigen III having toxic properties with the use of the indirect immunoferritin technique. Antigen III was localized in the outer fibrillar microcapsule-like layer 12-20 mm thick. In the direct immunoperoxidase test antigen III had globular localization on the cell wall surface. The layer described is unlikely to be a true microcapsule, since it does not contain acid mucopolysaccharides and is readily removed from the cell. It is more likely that it forms as a result of antigen III secretion (and, possibly, of other antigens) being more similar to a capsule-like or mucilagenous layer.