ONTOGENY AND DISTRIBUTION OF THE MURINE B-CELL FC-GAMMA-RII

The distribution and expression of the IgG FcRII (Fc-gamma-RII) on normal murine B cells was examined. Using multicolor flow cytometry, spleens from neonatal mice of increasing age and adult bone marrow were analyzed for expression of the Fc-gamma-RII. In addition, B cells from peripheral lymphoid organs, as well as a panel of B cell tumors, were tested. The results demonstrate that the Fc-gamma-RII is expressed on all pre-B cells and immature B cells in the neonatal spleen and adult bone marrow, on all mature B cells in peripheral lymphoid organs, and on switched B cells in Peyer's patches. Furthermore, the Fc-gamma-RII was found to be present on B cell tumors representative of all stages of B cell maturation and differentiation. Taken together, the results indicate that Fc-gamma-RII is expressed during the entire lifetime of the B cell. In addition, examination of spleen cells from neonatal mice revealed a large number of pre-B cells, phenotypically defined as B220+, IgM-. These pre-B cells were present at birth, peaked in number between 2 and 3 wk of age, and became a minor population by day 30. Further phenotypic analysis of these cells demonstrated the expression of the BLA-1 and BP-1 Ag, and the lack of T cell and NK cell markers, thus confirming their assignment to the B cell lineage. Finally, the Fc-gamma-RII present on these pre-B cells was shown to be functional, by virtue of its ability to bind aggregated IgG.