Variable cross-reactivity of Pseudomonas aeruginosa lipopolysaccharide-code-specific monoclonal antibodies and its possible relationship with serotype.

The core region of Pseudomonas aeruginosa lipopolysaccharide (LPS) was analysed by four LPS-core-specific human monoclonal antibodies (mAbs; FK-2E7, MH-4H7, OM-1D6 and NM-3G8). Reactivity of these mAbs to about 180 P. aeruginosa strains was tested. FK-2E7 bound to strains of Homma serotype E and I at a frequency of about 90%, to strains of serotype M at about 50%, and to strains of serotype A and G at about 30%. MH-4H7 bound to P. aeruginosa strains of serotype A, F, G, H, K and M at a high frequency (45-87%), but did not bind to any strains of serotype B, C, E and I. OM-1D6 and NM-3G8 bound to P. aeruginosa strains in a nearly serotype-specific manner. OM-1D6 reacted with all strains of serotype G so far tested, and a few strains of serotype M. Furthermore, L-rhamnose in the LPS core of serotype G was an immunodominant sugar recognized by OM-1D6 as an epitope. NM-3G8 bound to only a few strains of serotype B and M. The variable reactivity of these mAbs suggests that antigenic heterogeneity of the LPS core is somewhat related with (O-polysaccharide-based) serotype. Among these mAbs, MH-4H7 and OM-1D6 showed a high level of protective activity against P. aeruginosa in an experimental infection model using normal mice. In vivo protective activity was shown to be closely related to in vitro binding activity to whole cells as determined by agglutination and flow cytometry, but not ELISA.