Two species of human Fc epsilon receptor II (Fc epsilon RII/CD23): tissue-specific and IL-4-specific regulation of gene expression.

The Fc epsilon receptor II (Fc epsilon RII, CD23) functions in B cell growth and differentiation and in IgE-mediated immunity. The Fc epsilon RII structure expressed on various cell types has been analyzed identifying two species, Fc epsilon RIIa and Fc epsilon RIIb. 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 Fc epsilon RII species appear to be generated utilizing different transcriptional initiation sites and alternative RNA splicing. Fc epsilon RIIa is constitutively expressed only in normal B cells and B cell lines, whereas Fc epsilon RIIb expression is detectable in various cell types, such as monocytes and eosinophils. Normally, Fc epsilon RIIb is undetectable in B cells and monocytes, and can be induced by interleukin-4. Moreover, Fc epsilon RIIb is expressed on peripheral blood lymphocytes in atopic individuals. These findings may explain the difference in Fc epsilon RIIa and Fc epsilon RIIb function in B cells and the effector phase of IgE-mediated immunity.