Continuous Free-Flow Fractionation of Cellular Constituents in Rat Bone Marrow

A single-cell suspension of normal rat bone marrow is prepared mechanically. This suspension is continuously fractionated in free solution, under sedimentation rate conditions, using 1 g. only. With a sample flow of 2.2 x 10⁶ cells/minute and a 32-minute steady-state residence time in the stable-flow free boundary (STAFLO) flow-cell, the cells exit almost entirely into 7 of the 12 collection bottles. Maximum numbers of different cell types are observed, with good repeatability, in approximately descending order from top to bottom as follows: erythrocytes, "erythroblasts," "immatures," "myelocytes," and mature granulocytes. Major changes are effected relative to the starting marrow composition, and large relative enrichments are achieved for certain cell types. In addition to the rapid, mild, preparative aspect of this study, nominal sedimentation rates can be assigned for the different collection fractions, in the range of 3 x 10⁵ to 4 x 10⁶ svedbergs, thus making a start on this kind of simple physical classification of the cellular elements in this complex tissue.