Opsonic effect of monoclonal antibodies against Leptospira interrogans serovar copenhageni.

The opsonic effect of monoclonal antibodies (McAbs) against Leptospira interrogans serovar copenhageni strain Shibaura was examined in vitro using radiolabeled organisms and mouse peritoneal exudate macrophages. Four IgG McAbs (all IgG3) and 2 IgM McAbs were used, all showed different reactivities and were bound to homologous lipopolysaccharide (LPS). IgG3 McAbs at the sub-agglutinating concentration were opsonic, but the degree of the opsonic effect varied among IgG3 McAbs. Opsonization with IgG3 McAbs at the concentration showing the same level of ELISA binding showed that the highest opsonic effect was exerted by Sw-6 antibody. The other IgG3 McAbs showed a similar but lower opsonic effect. IgM McAbs, which were not opsonic at the sub-agglutinating concentration even in the presence of complement, showed opsonic effect at the agglutinating concentration.