Maturation of bone marrow lymphocytes. I. Quantitative rosetting methods of detecting Fc and complement receptors and surface immunoglobulin.

Cytocentrifuge rosetting procedures were developed for use with bone marrow cells to quantitate Fc and complement receptors (FcR, CR) and surface IgM on marrow small lymphocytes. Cell suspensions from 9–11-week-old C3H mice were mixed (1 : 30) with washed sheep red blood cells (SRBC) coated with either mouse anti-SRBC serum (for FcR), rabbit anti-SRBC stroma serum plus mouse serum (for CR) or goat anti-mouse IgM serum (for IgM). Centrifuged cell pellets were incubated for 30 min at either 37°C (FcR, CR) or 0°C (IgM) and examined in stained cytocentrifuge preparations. Small lymphocytes were defined as non-DNA-synthesizing lymphocytes smaller than 10 μm nuclear diameter. Many of these cells in the bone marrow formed specific rosettes for FcR (25%), CR (18%) and surface IgM (39%). The incidence of FcR- and CR-bearing small lymphocytes relative to IgM-bearing small lymphocytes was lower in the marrow than in the blood, spleen and lymph nodes. Rosette size ranged from 4 to > 20 SRBC per lymphocyte but tended to be smaller in the marrow and blood than in the spleen and lymph nodes. The methods and results are discussed as a basis for studies of B lymphocyte maturation and lymphocyte heterogeneity in the bone marrow.