Signal transduction pathways triggered by the FcϵRIIb receptor (CD23) in human monocytes lead to nuclear factor-κB activation

Abstract

Background: Alveolar macrophages play a key role in the initiation of the inflammatory reaction of allergic asthma. Alveolar macrophages and peripheral blood monocytes are activated when IgE/allergen immune complexes bind to the CD23 receptor, which leads to the production of inflammatory cytokines. Objective: We sought to investigate the molecular mechanisms regulating this early inflammatory response. We have focused on the study of the signal transduction pathways triggered by CD23 in human monocytes and the promonocytic cell line U937. Methods: CD23 was cross-linked in human monocytes and U937 cells with IgE immune complexes. Surface expression of CD23 was determined by FACS analysis. Transcription factor activation and gene transcription were studied by gel-shift assays and Northern blot analysis, respectively. IκBα phosphorylation and degradation was analyzed by Western blot. Results: Nuclear factor (NF)-κB is the main transcription factor involved in the gene activation that follows CD23 cross-linking in monocytes. CD23-induced NF-κB is a heterodimer composed of p65/p50 subunits. NF-κB nuclear translocation is secondary to the phosphorylation and subsequent degradation of the NF-κB inhibitory molecule IκBα. Tyrosine kinase–dependent, and not protein kinase C–dependent, pathways mediate CD23-triggered NF-κB activation but do not participate in the direct phosphorylation of IκBα. IκBα degradation and NF-κB nuclear translocation correlate with transcriptional activation of the inflammatory cytokines TNF-α and IL-1β. Conclusions: NF-κB is the main transcription factor involved in the signal transduction pathway of CD23 in monocytes. (J Allergy Clin Immunol 1999;104:376-87.)