Antibody response in rabbits to serotype-specific determinants in lipopolysaccharides from Moraxella catarrhalis

Antibodies against the serotype determinant epitopes of Moraxella catarrhalis lipopolysaccharides (LPS) were demonstrated in sera from rabbits immunised with whole bacterial cells. Purified LPS preparations from eight strains of M. catarrhalis were used as antigens in enzyme-linked immunosorbent assays (ELISA) and immunoblotting. The serotype specificity of the antibodies was shown by neutralisation with LPS and with purified polysaccharide obtained from LPS prepared from strains belonging to different serotypes. In immunoblots, antisera against the A and B LPS serotypes reacted only with LPS of its own type, confirming the presence of type-specific antibodies. A weak band was observed with type A LPS and antibody to type C, indicating cross-reactivity between the A and C serotypes. This cross-reaction can be explained on the basis of the known chemical structure of the LPS of the different serotypes. After heterologous absorption of sera, bands were obtained with homologous LPS antigen. These results suggest that the predominant antibody response in rabbits to LPS from M. catarrhalis is serotype-specific, unlike that previously observed in infected human patients.