Mouse B lymphocytes have separate surface receptors for mouse C3b and C3d, but study of their function has been hampered by a lack of indicator particles completely specific for each receptor type.
We report here that mouse spleen lymphocytes will bind to guinea pig (GP) C3b but not to GP C3d, so any possible contamination of the indicator cells with C3d should be of little consequence. There was no binding to GP C4. Indicator cells were prepared from EAC142 GP and purified GP C3. They were maximally reactive in I-A, unreactive with bovine conglutinin, and rosetted with about 27% of mouse and GP spleen cells. When these EAC43b were incubated for 40 min at 0°C in EDTA with heated GP serum, there was little or no change in their I-A activity, but they lost completely the ability to rosette with mouse (but not GP) lymphocytes; their C3 hemolytic activity was markedly reduced; and they gained the capacity to be agglutinated by bovine conglutinin.