Recognition of the viral particle is important. Cotton rats were inoculated intraperitoneally with 1 mL of antibody with a neutralization titer of 320 (MV-specific IgG and K4, K17, K71, and K83) or 2 mg of F227. MV-specific IgG recognizes the fusion, hemagglutinin, and nucleocapsid proteins of MV and neutralizes MV. Monoclonal antibodies K4, K17, K71, and K83 recognize different epitopes on MV hemagglutinin and neutralize MV. Monoclonal antibody F227 recognizes MV-N and does not neutralize. One day later, cotton rats were immunized subcutaneously with 105 pfu MV (Schwarz strain). Results are mean ± SD of 4 cotton rat per group. (A) Neutralizing antibody responses were determined from cotton rat serum 7 weeks after immunization. At this time point, human antibodies are not detectable by ELISA (data not shown). Animals immunized in the presence of MV-H-specific antibodies generated significantly fewer antibodies. **P < .01. ***P < .001. (B) The MV-N–specific antibody response was determined 7 weeks after immunization from cotton rat sera by ELISA using purified MV-N as antigen. Both polyclonal MV-specific IgG (*P < .05) and F227 (**P < .01) significantly inhibited the generation of N-specific antibodies. (C) Sera from cotton rats immunized in the absence of antibody or immunized in the presence of monoclonal antibodies K71, K83, or L77 were used to block MV antigen coated to an ELISA plate. Subsequently, K71, K83, or L77 antibodies were added to determine whether the respective epitopes recognized by these antibodies were masked by the sera.
