Early precursors of B lymphocytes. II. Exploitation of the singular properties of rabbit pre-B cells in their purification.

Rabbit pre-B cells are almost uniformly large and low in density and bear a modest number of Fc receptors (McElroy, P.J., Willcox, N. and Catty, D., Eur. J. Immunol. 1981. 11:76). A simple density gradient centrifugation procedure consistently and rapidly enriches them to 20-35% frequencies. At the same time, it depletes them of most of the B cells, phagocytic and erythroid cells that are also common in bone marrow, and are of progressively higher densities. The low-density fractions include 45-55% of large blast-like cells and have 35-45% of cells with Fc receptors. By isolating the large Fc receptor-bearing cells from low-density fractions of baby rabbit bone marrow on a fluorescence-activated cell sorter, pre-B cells were obtained at approximately 60% frequency and virtually uncontaminated by B cells (or plasma cells). This level of purity is perhaps adequate for the critical experiments necessary to establish the precursor status of pre-B cells definitively, and it might also prove valuable for studying the mechanisms of the genetic rearrangements that occur in early B cell development.