Western blot of the binding patterns of IgM MAbs 1G4 and 4F11 and of the IgG1 switch variant of MAb 4F11, 4F11(G1). Lanes 1, 3, and 5 contain homogenized P. carinii-infected mouse lung, while lanes 2, 4, and 6 contain homogenized normal mouse lung. Molecular mass markers are noted in kilodaltons.