Characterization of immunoglobulin-bearing and other small lymphocytes in mouse bone marrow by sedimentation and electrophoresis.

125I-antiglobulin binding and radioautography have been used to define the sedimentation and electrophoretic properties of immunoglobulin-bearing and other small lymphocytes in bone marrow. Bone marrow cell suspensions from CBA mice were exposed to 125I-labeled rabbit anti-mouse immunoglobulin for 30 min at 0 degrees C. Cell fractions were collected after either sedimentation at unit gravity or continuous free-buffer film preparative electrophoresis. The sedimentation profiles of labeled, antiglobulin-binding small lymphocytes and of unlabeled small lymphocytes were identical, peaking at 2.6 mm/hr, except for 5% of the labeled small lymphocytes which sedimented at 3.8 to 4.1 mm/hr. In electrophoretic fractions most labeled small lymphocytes were contained in a peak of low mobility and unlabeled small lymphocytes were of intermediate mobility, but high mobility fractions also contained small numbers of labeled and unlabeled small lymphocytes. Small lymphocytes comprised 80 to 85% of all nucleated bone marrow cells in fractions taken at the peak of the small lymphocyte distribution profile after either sedimentation or electrophoresis, accompanied mainly by either erythroid or granulocytic precursor cells, respectively. The results demonstrate that small lymphocytes with readily detectable surface immunoglobulin in the bone marrow closely resemble those in peripheral lymphoid tissues with respect to their sedimentation and electrophoretic properties. The possibility is raised that the rapidly sedimenting immunoglobulin-bearing small lymphocytes in bone marrow are a functionally distinct group of potential precursor cells. Non-antiglobulin-binding small lymphocytes in bone marrow resemble electrophoretically the double negative (immunoglobulin -and theta -negative) small lymphocytes in other lymphoid tissues. Small lymphocytes of high electrophoretic mobility, prominent in the theta- bearing lymphocyte populations of peripheral lymphoid tissues, are few in bone marrow. Lymphocyte-rich suspensions, containing either high or low proportions of immunoglobulin-bearing small lymphocytes, can be separated from bone marrow by electrophoresis