Pre-B cells in bone marrow: size distribution profile, proliferative capacity and peanut agglutinin binding of cytoplasmic mu chain-bearing cell populations in normal and regenerating bone marrow.

Pre-B cell populations in mouse bone marrow, identified by double immunofluorescence labelling of cytoplasmic and surface mu chains (c mu, s mu), have been characterized by cell size, proliferative capacity and the binding of peanut agglutinin (PNA). In the normal steady state of lymphocyte production the size distribution profile of cytocentrifuged c mu + s mu- cells was bimodal. A population of large cells in rapid cell cycle was revealed by arresting cells in mitosis with vincristine. Many c mu + s mu- cells, however, formed a nondividing population of small lymphocytes, resembling s mu + cells in size distribution. During regeneration from sublethal whole body X-irradiation (150 rads) a marked enrichment of large c mu + s mu- cells preceded small c mu + s mu- and s mu + cells; progressive changes in cell size distribution reflected a wave of B lymphocyte genesis. The c mu + s mu- cells in foetal liver resembled those in regenerating marrow. Surface binding of PNA characterised all c mu + s mu- cell populations in normal and regenerating bone marrow and in foetal liver, whereas only a minority of s mu + cells and mu-negative marrow cells bound PNA strongly. The present size distribution analyses allow a correlation with other cytological and functional studies of marrow lymphocyte precursors in defining the place of pre-B cells in B lymphocyte genesis.