Pax-5 is a key regulator of the B cell-restricted expression of the CD23a isoform.

Human CD23 (the low affinity IgE receptor) is a B cell differentiation marker involved in inflammatory responses. Two isoforms (CD23a and CD23b) are known, which differ only in their cytoplasmic domain. Whereas CD23b expression is specifically induced by IL-4 on B cells and cells of the myeloid lineage, CD23a expression is restricted to B cells.

The CD23b promoter is a target for NF-AT transcription factors in B-CLL cells.

CD23 is atypically highly expressed in various chronic diseases, including B-CLL, lupus erythematodes and rheumatoid arthritis. Its expression can be further enhanced by interleukin 4 (IL-4). We have shown before that in B-CLL cells nuclear factor(s) of activated T cells (NF-ATs) show permanent nuclear localization and therefore constitutive transcriptional activity.

Regulation of CD23 isoforms on B-chronic lymphocytic leukemia.

CD23 is constitutively and atypically expressed on malignant B-cells in patients with chronic lymphocytic leukemia. It exists in two isoforms that differ only in a short amino acid sequence at the N-terminus. The CD23a isoform exhibits an endocytosis signal, that renders it more efficient in antigen uptake than CD23b.