CHARACTERIZATION OF MURINE MONOCLONAL-ANTIBODIES RECOGNIZING OPSONIC,MOUSE-PROTECTIVE, CHAINING AND MUCOSALLY RELEVANT EPITOPES ON THE M-PROTEIN OF STREPTOCOCCUS-EQUI SUBSPECIES EQUI

Six hybridomas secreting murine monoclonal antibodies (mAbs) specific for the M protein of Streptococcus equi subspecies equi were character ised. The mAbs recognised the major 41 and 46 kDa fragments of M prote in in an acid extract of S equi and the 56 and 58 kDa dimer of the nat ive molecule in a mutanolysin extract, but did not react with recombin ant M-like protein of S equi subspecies zooepidemicus. One mAb (2A10) showed strong opsonic activity for S equi and protected mice against a n experimental challenge with virulent S equi. Two other mAbs were mou se-protective but not opsonic. All the mAbs elicited a strong chaining response from S equi, but had only a weak chaining effect on a strain of S equi (19) that expressed only 4 per cent of the normal amount of M protein. Antibodies in nasopharyngeal mucus of horses recently reco vered from strangles were inhibited to different extents by each mAb. These different functional behaviours and the result of inhibition ELI SAs suggest that the M protein of S equi carries multiple epitopes.