Two species of human Fcε receptor II (FcεRIICD23): Tissue-specific and IL-4-specific regulation of gene expression

Abstract The Fce receptor II (FceRII, CD23) functions in B cell growth and differentiation and in IgE-mediated immunity. The FceRII structure expressed on various cell types has been analyzed identifying two species, FceRIIa and FceRIIb. Sequence analysis of the cloned cDNAs revealed that they differ only at the N-terminal cytoplasmic region, but share the same C-terminal extracellular region. These FceRII species appear to be generated utilizing different transcriptional initiation sites and alternative RNA splicing. FceRIIa is constitutively expressed only in normal B cells and B cell lines, whereas FceRIIb expression is detectable in various cell types, such as monocytes and eosinophils. Normally, FceRIIb is undetectable in B cells and monocytes, and can be induced by interleukin-4. Moreover, FceRIIb is expressed on peripheral blood lymphocytes in atopic individuals. These findings may explain the difference in FceRIIa and FceRIIb function in B cells and the effector phase of IgE-mediated immunity.