The response to anti-allotype (anti-Ab4), Nocardia Water Soluble Mitogen (NWSM), pneumococcal polysaccharide type III (SSS III), and human Fc fragments of various purified and unfractionated rabbit spleen cell populations was determined in terms of 3H-thymidine uptake. B cells were isolated either from untreated suspensions of spleen cells or from suspensions from which adherent and phagocytic cells were removed. The purification factor was greater than the enhancement of 3H-thymidine uptake by anti-Ab4, NWSM, and SSS III as compared with the response of unfractionated spleen cells. It thus appears that a helper cell was involved: the mitogen response of purified B cells was enhanced by the addition of T cells. B subpopulations were separated by sedimentation or by rosetting, which allowed us to separate Fcγ receptor-bearing cells from cells that did not possess this receptor. There were differences between cells responding to B mitogens not only in sedimentation velocity but also in the absolute number of cells. B cells bearing the Fcγ receptor were less responsive to anti-Ab4 and more responsive to SSS III, NWSM, and human Fc than were B cells lacking the Fcγ receptor.


This work was supported by grants from the Medical Research Council and the National Cancer Institute of Canada.

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