Antibodies inhibit B cells through the Fc region. (A) Bone marrow cells from an MV-immune cotton rat were stimulated with MV antigen in an ELISPOT assay, and complete IgG or the respective F(ab′)2 fragment was added at a neutralization titer (NT) of 0.5. For some wells, IgG specific for mouse F(ab′)2 fragments was added after 1 hour of incubation with the F(ab′)2 fragment. The reduction in numbers of responding B cells was significant after addition of complete IgG or the F(ab′)2-anti-F(ab′)2 complex. *P < .05. **P < .01. (B) Cotton rats were inoculated intraperitoneally with 1 mL (100NT) of human MV-specific IgG or 1 mL (200NT) of human F(ab′)2 fragments and were immunized with 105 pfu MV (Schwarz strain) subcutaneously 4 hours later. Four weeks after immunization, the generation of neutralizing antibodies was tested by neutralization assay. *Complete IgG significantly suppressed the generation of neutralizing antibodies (P < .05).
