The Lymphocyte Production Pathway in Bone Marrow: Possible Significance of the Size Spectrum of Lymphocytes and their Precursors

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Abstract
It is now generally accepted that transitional (lymphoid) cells are the precursors of small lymphocytes. Such cells have a heterogeneous size spectrum and show high proliferative capacity. To facilitate the study of the kinetics of lymphocyte production, a detailed investigation of cell sizes of the transitional cell-lymphocyte compartment was carried out using a Coulter counter modified to permit a very rapid and accurate examination of cells in suspension. Enriched populations of [guinea pigs] lymphoid cells, obtained after 10 days rebound from hypoxia at 1/2 an atmosphere were enriched further by bovine albumin and Ficoll gradients to give density fractions containing 2 types of cells. Differential counts of stained smears of these fractions enabled a comparison to be made between the size distribution and the specific type cells. Four distinct cell types were characterized in terms of volume and density: small and intermediate-sized lymphocytes (volume 53-59 f[femto]l, albumin fractions 19-23%), small transitional cells (154-160 fl, 21-23%), medium transitional cells (206-218 fl, 17-19%) and large transitional cells (350-400 fl, 21-27%). These findings were consistent with the view that there are at least 3 mitoses in the course of the lymphocyte production pathway in the bone marrow.
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