Soluble CD23 potentiates interleukin-1-induced secretion of interleukin-6 and interleukin-1 receptor antagonist by human monocytes.

The low-affinity receptor for IgE (CD23) is cleaved into biologically active soluble fragments (sCD23), some of which have been reported to exhibit pleiotropic activities. However, it is not known whether the sCD23 fragments contribute to the induction and/or regulation of pro-inflammatory cytokine production. In this study, this possibility was tested using interleukin (IL)-1-stimulated human whole blood as an ex vivo model of cytokine cascade production. We show that human recombinant 25-kDa sCD23 significantly enhanced the production of IL-6 in whole blood stimulated by IL-1, but had only little or no effect in the absence of IL-1. The potentiating effect of sCD23 was concentration dependent within the range of plasma levels occurring during various inflammatory processes in man. These results prompted us to study whether sCD23 and IL-1 together also enhance the production of regulating factors exhibiting anti-cytokine activities. Our data indicate that sCD23 augments the release of IL-1 receptor antagonist induced by IL-1. Finally, examining the effect of sCD23 on human peripheral monocytes stimulated by IL-1, we confirmed the capacity of sCD23 to potentiate cytokine production. We suggest that sCD23 can modulate monocyte functions, thereby contributing to the amplification and regulation of immune and inflammatory processes.