The Fc epsilon RII/CD23 gene is actively transcribed during all stages of murine B-lymphocyte development

It is generally accepted that the expression of Fc epsilon RII/CD23 on the surface of the B-lineage cells is restricted to the stage of the resting, mature (sIgM+/sIgD+) B-lymphocyte. However, it is unknown whether activation of the Fc epsilon RII/CD23 gene is also restricted to the stage of the mature B-lymphocyte. To address this question we investigated a panel of B-lineage cell lines for the presence of transcripts encoding Fc epsilon RII/CD23. We detected transcripts in 16 of 26 B-lineage cell lines representing the entire spectrum of B-cell development. In most cases (13 of 16) active transcription of the murine Fc epsilon RII/CD23 gene was not coupled with the expression of cell surface Fc epsilon RII/CD23 expression did not hold for all murine B-cell lines. One post-switch B-cell line (sIgM-/sIgG+) expressed Fc epsilon RII/CD23 on the cell surface and another could be induced with IL-4 and LPS to express surface Fc epsilon RII/CD23. Transcription of the murine CD23 gene in the absence of cell surface expression of Fc epsilon RII/CD23 does not appear to simply be an aberrant feature of transformed B-cells since we found transcripts, but not surface expression, in some normal splenic and peritoneal B-lymphocytes. Our findings suggest that the potential for expression of Fc epsilon RII/CD23 may occur over a much broader development window of the B-lineage than previously suspected. Transcription of the Fc epsilon RII/CD23 gene, in the absence of detectable cell surface protein expression in B-lineage cell lines, and in sort-purified B-lymphocyte subpopulations, implies that in addition to regulatory mechanisms already known, murine CD23 is also regulated through post-transcriptional mechanisms that have not yet been characterized.