Influence of bispecific antibodies on the in vitro bactericidal activity of bovine neutrophils against Staphylococcus aureus

We conducted the following study to determine if bispecific antibodies enhance the bactericidal activity of bovine neutrophils. Bispecific antibodies were synthesized by chemically crosslinking bovine neutrophil monoclonal antibodies to Staphylococcus aureus 305 capsule polysaccharide monoclonal antibodies. The efficiency of chemically coupling monoclonal antibody monomers was approximately 50% for each bispecific antibody produced. Monoclonal antibodies against neutrophils enhanced the respiratory burst activity of neutrophils by 2.3- to 2.5-fold. To determine the influence of bispecific antibodies on neutrophil function, S. aureus 305 was preincubated with various concentrations of bispecific antibodies and neutrophils were then added to the opsonized bacteria at different bacteria to neutrophil ratios. The bactericidal activity of neutrophils was expressed as a percentage reduction in colony-forming units in test cultures compared with the number of colony-forming units in control test cultures that did not contain bispecific antibodies or neutrophils. The addition of bispecific antibodies to test cultures increased the bactericidal activity of neutrophils. A reduction in colony-forming units as a function of increasing the S. aureus 305 to neutrophils ratio was observed in both the absence and presence of bispecific antibodies. However, a greater reduction was observed in the presence of bispecific antibodies. Increasing concentrations of bispecific antibodies enhanced the bactericidal activity of neutrophils at a constant S. aureus 305 to neutraphil ratio of 1:500. The results indicate that bispecific antibodies that recognize both S. aureus 305 capsular polysaccharide and neutrophil antigens potentiate the bactericidal activity of neutrophils.