Therapeutic implications of the IL-21: IL-4 receptor system in children with common variable immunodeficiency syndrome.

OBJECTIVES: Interleukin-21 (IL-21) has been shown to restore immunoglobulin production together with Interleukin-4 (IL-4) in common variable immunodeficiency syndrome (CVID). Here, we elucidate the functional and structural properties of the corresponding IL-21R : IL-4R system. PATIENTS AND METHODS: An in vitro cell culture system was established to study the molecular effects of IL-21 and IL-4 on B cell differentiation, class-switch recombination (CSR) and immunoglobulin (Ig) production in 32 paediatric patients with CVID. MHC haplotypes and the IL21 and IL21R gene were analysed by genotyping. Ternary complexes of the IL-21 respectively IL-4 receptor were set-up by homology modeling and ligand-interaction was examined by molecular dynamics (MD) simulation. RESULTS: Stimulation with IL-21, IL-4 and CD40L uniformly induced IgG and IgA production in B cells from all tested patients by initiation of both CSR and AID-independent Ig production. No mutations were found in the coding regions of the IL21 or IL21R genes and no distinct HLA allele or extended haplotype could be correlated with the amount of Ig production or the gene expression pattern induced by IL-21. MD simulations of the modelled receptor complexes showed that IL-4 and IL-21 are both able to bind to IL-4R and IL-21R complexes in an interchangeable manner. CONCLUSIONS: The function of the IL-21R : IL-4R system seems not to be related to the aetiology of CVID in paediatric patients and might be suitable for a regenerative therapy.

Heterogeneous expression and function of IL-21R and susceptibility to IL-21-mediated apoptosis in follicular lymphoma cells.

OBJECTIVE: Interleukin (IL)-21, a member of the IL-2 family, has antitumor activity and is now being tested in non-Hodgkin's lymphoma in combination with anti-CD20 antibodies. IL-21 may either induce apoptosis or promote growth in different lymphoid malignancies. We therefore investigated the IL-21/IL-21R system in follicular lymphoma (FL) cells. MATERIALS AND METHODS: IL-21R expression was studied by reverse transcription polymerase chain reaction, immunofluorescence, and Western blot analyses. Apoptosis was measured by Annexin-V-propidium iodide staining. Signaling via IL-21R was studied using antibodies specific for phosphorylated Janus-activating kinase and signal transducers and activators of transcription proteins by Western Blot. RESULTS: IL-21R was found on primary FL cells in 15 of 15 cases at diagnosis and IL-21 increased apoptosis in 10 of 10 FL samples. However, cells from areas of diffuse growth in FL and from two diffuse lymphomas evolved from previous FL, showed low IL-21R expression. The latter were also resistant to IL-21-mediated apoptosis. Among lymphoma cell lines bearing the t(14;18) translocation, only 1 of 7 showed increased apoptosis in response to IL-21 stimulation. This cell line was IL-21R-positive, whereas five of six nonresponsive cell lines showed very low IL-21R expression. Intriguingly, one of the IL-21-resistant cell lines (DOHH2) expressed high levels of IL-21R. Treatment with IL-21 or IL-4 upregulated suppressor of cytokine signaling 3 gene expression in the IL-21-responsive cell line, but not in DOHH2 cells, which showed defective Janus-activating kinase/signal transducers and activators of transcription signaling in response to IL-21, in relationship to the lack of Janus-activating kinase 3 gene expression. CONCLUSION: These data indicate that low IL-21R expression or defective signal transduction downstream IL-21R may cause refractoriness to IL-21-mediated effects in some FL cells.