Molecular Blocking of CD23 Supports Its Role in the Pathogenesis of Arthritis

BACKGROUND: CD23 is a differentiation/activation antigen expressed by a variety of hematopoietic and epithelial cells. It can also be detected in soluble forms in biological fluids. Initially known as the low-affinity receptor for immunoglobulin E (Fc epsilonRII), CD23 displays various other physiologic ligands such as CD21, CD11b/c, CD47-vitronectin, and mannose-containing proteins. CD23 mediates numerous immune responses by enhancing IgE-specific antigen presentation, regulating IgE synthesis, influencing cell differentiation and growth of both B- and T-cells. CD23-crosslinking promotes the secretion of pro-inflammatory mediators from human monocytes/macrophages, eosinophils and epithelial cells. Increased CD23 expression is found in patients during allergic reactions and rheumatoid arthritis while its physiopathologic role in these diseases remains to be clarified. METHODOLOGY/PRINCIPAL FINDINGS: We previously generated heptapeptidic countrestructures of human CD23. Based on in vitro studies on healthy and arthritic patients' cells, we showed that CD23-specific peptide addition to human macrophages greatly diminished the transcription of genes encoding inflammatory cytokines. This was also confirmed by significant reduction of mediator levels in cell supernatants. We also show that CD23 peptide decreased IgE-mediated activation of both human and rat CD23(+) macrophages. In vivo studies in rat model of arthritis showed that CD23-blocking peptide ameliorates clinical scores and prevent bone destruction in a dose dependent manner. Ex-vivo analysis of rat macrophages further confirmed the inhibitory effect of peptides on their activation. Taken together our results support the role of CD23 activation and subsequent inflammatory response in arthritis. CONCLUSION: CD23-blocking peptide (p30A) prevents the activation of monocytes/macrophages without cell toxicity. Thus, targeting CD23 by antagonistic peptide decreases inflammatory markers and may have clinical value in the treatment of human arthritis and allergic reactions involving CD23

Soluble CD40 ligand induces β(3) integrin tyrosine phosphorylation and triggers platelet activation by outside-in signaling

We earlier reported that the soluble form of the CD40 ligand (sCD40L), is involved in thrombosis by stabilizing platelet thrombi. In this article, we have determined the mechanism by which this protein affects platelet biology. Addition of sCD40L to washed platelets was found to activate the receptor function of α(IIb)β(3) as measured by the induction of fibrinogen binding and the formation of platelet microparticles. Mutation in the KGD sequence (D117E) of sCD40L, the α(IIb)β(3)-binding domain in the N terminus of the protein resulted in a loss of the platelet-stimulatory activity of this protein. Integrilin, a α(IIb)β(3) antagonist, but not an antibody to CD40 that blocked the ligand-binding activity, inhibited these platelet-stimulatory events. CD40(-/-) platelets bound fibrinogen and formed microparticles similar to WT platelets, again indicating that CD40 is not involved in sCD40L-induced platelet activation. Exposure of platelets to sCD40L, but not D117E-sCD40L-coated surfaces, induced platelet thrombi formation under arterial shear rate. sCD40L-induced platelet stimulation resulted in the phosphorylation of tyrosine-759 in the cytoplasmic domain of β(3). Platelets from the diYF mouse strain, expressing β(3) in which both cytoplasmic tyrosines are mutated to phenylalanine, were defective in sCD40L-induced platelet stimulation. These data indicate that sCD40L is a primary platelet agonist and that platelet stimulation is induced by the binding of the KGD domain of sCD40L to α(IIb)β(3), triggering outside-in signaling by tyrosine phosphorylation of β(3)

Expression of CD21 and CD23 during human fetal development

Neonates produce lower levels of IgE compared with adults. Diminished IL-4 production and impaired up-regulation of CD40L by neonatal T cells could explain this, however other regulators of IgE production, such as CD21 and CD23, could contribute to reduced circulating IgE levels during fetal development. Heparinized blood samples were collected from adults and from the umbilical cord at premature and term births. Whole blood flow cytometry was used to assess the percentage of T (CD3+) and B (CD19+) lymphocytes expressing CD21 and/or CD23 at 26–29 (n = 3), 30–33 (n = 7), 34–37 (n = 5), and >37 (n = 11) wk of gestation, as well as in adults (n = 15). Plasma-soluble CD21 was also measured. At term, the percentage of CD21+ and CD23+ B cells was comparable to the adult, however, the percentage of cells positive for each of these surface antigens was decreased significantly before term. The percentage of T cells expressing CD21 from all gestations was significantly higher than the adult and the percentage positive decreased with increasing gestational age. Conversely, soluble CD21 levels increased with increasing gestation to be comparable to the adult by term. Thus, it is unlikely that altered expression of CD21 and CD23 on B cells contributes to the low level of IgE in the neonatal circulation unless functional differences occur or a lack of processing to the soluble form is important in regulating IgE production. However the abundance of CD21-positive T cells could alter the T- and B-cell interaction necessary for IgE switching by B cells and, thereby, especially with impaired IL-4 production, limit IgE production