RESUMEN
CD23, the low-affinity receptor for IgE, exists in membrane and soluble forms. Soluble CD23 (sCD23) fragments are released from membrane (m)CD23 by the endogenous metalloprotease a disintegrin and metalloprotease 10. When purified tonsil B cells are incubated with IL-4 and anti-CD40 to induce class switching to IgE in vitro, mCD23 is upregulated, and sCD23 accumulates in the medium prior to IgE synthesis. We have uncoupled the effects of mCD23 cleavage and accumulation of sCD23 on IgE synthesis in this system. We show that small interfering RNA inhibition of CD23 synthesis or inhibition of mCD23 cleavage by an a disintegrin and metalloprotease 10 inhibitor, GI254023X, suppresses IL-4 and anti-CD40-stimulated IgE synthesis. Addition of a recombinant trimeric sCD23 enhances IgE synthesis in this system. This occurs even when endogenous mCD23 is protected from cleavage by GI254023X, indicating that IgE synthesis is positively controlled by sCD23. We show that recombinant trimeric sCD23 binds to cells coexpressing mIgE and mCD21 and caps these proteins on the B cell membrane. Upregulation of IgE by sCD23 occurs after class-switch recombination, and its effects are isotype-specific. These results suggest that mIgE and mCD21 cooperate in the sCD23-mediated positive regulation of IgE synthesis on cells committed to IgE synthesis. Feedback regulation may occur when the concentration of secreted IgE becomes great enough to allow binding to mCD23, thus preventing further release of sCD23. We interpret these results with the aid of a model for the upregulation of IgE by sCD23.
Asunto(s)
Linfocitos B/inmunología , Regulación de la Expresión Génica/inmunología , Genes de Inmunoglobulinas , Inmunoglobulina E/biosíntesis , Receptores de IgE/inmunología , Proteínas ADAM/antagonistas & inhibidores , Proteína ADAM10 , Secretasas de la Proteína Precursora del Amiloide/antagonistas & inhibidores , Linfocitos B/metabolismo , Dipéptidos/farmacología , Retroalimentación Fisiológica , Homeostasis , Humanos , Ácidos Hidroxámicos/farmacología , Cambio de Clase de Inmunoglobulina , Recubrimiento Inmunológico , Proteínas de la Membrana/antagonistas & inhibidores , Proteínas de la Membrana/fisiología , Inhibidores de Proteasas/farmacología , Unión Proteica , Interferencia de ARN , ARN Interferente Pequeño/farmacología , Receptores de Complemento 3d/inmunología , Receptores de IgE/genética , Proteínas Recombinantes de Fusión/química , Proteínas Recombinantes de Fusión/farmacología , Solubilidad , Regulación hacia ArribaRESUMEN
The low affinity IgE receptor, CD23, is implicated in IgE regulation and the pathogenesis of allergic disease. CD23 is a type II integral membrane protein, comprising a lectin "head," N-terminal "stalk," and C-terminal "tail" in the extracellular sequence. Endogenous proteases cleave CD23 in the stalk and the tail to release soluble fragments that either stimulate or inhibit IgE synthesis in human B cells. The molecular basis of these paradoxical activities is not understood. We have characterized three fragments of CD23, monomeric derCD23, monomeric exCD23, and oligomeric lzCD23. We show that the monomers inhibit and the oligomer stimulates IgE synthesis in human B cells after heavy chain switching to IgE. CD23 fragments could be targets for therapeutic intervention in allergic disease.
