Western immunoblot of M. pneumoniae wild type (WT), mutant I-2, and C1R1. Approximately equal amounts of mycoplasma total protein were electrophoresed on an SDS–5 to 15% polyacrylamide gradient gel, transferred onto nitrocellulose, and probed with antibody against the C-terminal region of HMW2 (1:1,000 dilution). HMW2, truncated HMW2 (ΔHMW2), and P28 are indicated by arrowheads; size standards are indicated in kilodaltons.