Previously, a phase-variable epitope was detected in the virulent wild-type strain RC1 of Legionella pneumophila serogroup 1 subgroup OLDA using a lipopolysaccharide-speci®c monoclonal antibody, mAb 2625 [LuÈneberg, E., ZaÈhringer,U.,Knirel,., Steinmann,D.,Hartmann,M., Steinmetz, I., Rohde, M., Kohl, J. & Frosch, M. (1998) J. Exp. , 49±60]. In the present study, an isogenic mutant strain, termed 5215, was constructed by deletion of genes involved in the biosynthesis of the mAb 2625 epitope
