Antigen specific receptors on murine B cell lineage. 2. Different effect of rosette-forming cell depletion on IgM and IgG antibody forming cell precursors in primary and secondary response.

Spleen cells from unprimed mice or those primed with horse red blood cells (HRBC) were depleted of rosette-forming cells (RFC) with HRBC by the Ficoll-Hypaque density sedimentation, and the cells were examined in the adoptive transfer system whether they could raise IgM or IgG antibody-forming cells (AFC) after an immunization with HRBC. When spleen cells were pooled from unprimed mice, the response to HRBC of those depleted of RFC with HRBC (HRBC-RFC) was decreased to about a half in both IgM and IgG AFC. On the other hand, when spleen cells were from mice primed with HRBC, the response to HRBC of those depleted of HRBC-RFC was decreased dramatically to 1/20 of that of original cells in IgG AFC, but it was decreased to about a half in IgM AFC. In the time course of the response to HRBC of RFC-depleted spleen cells from mice primed with HRBC, an early IgG response was abolished but the late one was as high as that of untreated spleen cells. These results suggest that the depletion of RFC is most effective on the depletion of direct precursors of the secondary IgG AFC.