B cell–intrinsic signaling through IL-21 receptor and STAT3 is required for establishing long-lived antibody responses in humans

Engagement of cytokine receptors by specific ligands activate Janus kinase–signal transducer and activator of transcription (STAT) signaling pathways. The exact roles of STATs in human lymphocyte behavior remain incompletely defined. Interleukin (IL)-21 activates STAT1 and STAT3 and has emerged as a potent regulator of B cell differentiation. We have studied patients with inactivating mutations in STAT1 or STAT3 to dissect their contribution to B cell function in vivo and in response to IL-21 in vitro. STAT3 mutations dramatically reduced the number of functional, antigen (Ag)-specific memory B cells and abolished the ability of IL-21 to induce naive B cells to differentiate into plasma cells (PCs). This resulted from impaired activation of the molecular machinery required for PC generation. In contrast, STAT1 deficiency had no effect on memory B cell formation in vivo or IL-21–induced immunoglobulin secretion in vitro. Thus, STAT3 plays a critical role in generating effector B cells from naive precursors in humans. STAT3-activating cytokines such as IL-21 thus underpin Ag-specific humoral immune responses and provide a mechanism for the functional antibody deficit in STAT3-deficient patients

Induction of interferon-stimulated genes on the IL-4 response axis by Epstein-Barr virus infected human b cells; relevance to cellular transformation.

Epstein-Barr virus (EBV) is an oncogenic virus that is associated with the pathogenesis of several human lymphoid malignancies, including Hodgkin's lymphoma. Infection of normal resting B cells with EBV results in activation to lymphoblasts that are phenotypically similar to those generated by physiological stimulation with CD40L plus IL-4. One important difference is that infection leads to the establishment of permanently growing lymphoblastoid cell lines, whereas CD40L/IL-4 blasts have finite proliferation lifespans. To identify early events which might later determine why EBV infected blasts go on to establish transformed cell lines, we performed global transcriptome analyses on resting B cells and on EBV and CD40L/IL-4 blasts after 7 days culture. As anticipated there was considerable overlap in the transcriptomes of the two types of lymphoblasts when compared to the original resting B cells, reflecting common changes associated with lymphocyte activation and proliferation. Of interest to us was a subset of 255 genes that were differentially expressed between EBV and CD40L/IL-4 blasts. Genes which were more highly expressed in EBV blasts were substantially and significantly enriched for a set of interferon-stimulated genes which on further in silico analyses were found to be repressed by IL-4 in other cell contexts and to be up-regulated in micro-dissected malignant cells from Hodgkin's lymphoma biopsies when compared to their normal germinal center cell counterparts. We hypothesized that EBV and IL-4 were targeting and discordantly regulating a common set of genes. This was supported experimentally in our B cell model where IL-4 stimulation partially reversed transcriptional changes which follow EBV infection and it impaired the efficiency of EBV-induced B cell transformation. Taken together, these data suggest that the discordant regulation of interferon and IL-4 pathway genes by EBV that occurs early following infection of B cells has relevance to the development or maintenance of an EBV-associated malignancy

Roles for the interleukin-4 receptor and associated JAK/STAT proteins in human articular chondrocyte mechanotransduction

SummaryObjectiveTo identify functional interleukin-4 (IL4) receptor (IL4R) subtypes and associated Janus kinase/signal transducers and activators of transcription (JAK/STAT) molecules in human articular chondrocytes and assess the role of JAK/STAT proteins in chondrocyte mechanotransduction.MethodsExpression of IL4R subunits and associated molecules was assessed by immunohistochemistry and western blotting. Functional IL4R were identified by chemical crosslinking of IL4-stimulated chondrocytes and western blotting. JAK and STAT phosphorylation was assessed by western blotting.ResultsChondrocytes from normal and osteoarthritic (OA) cartilage express IL4Rα, γc and IL13Rα1 subunits (components of the Type I and Type II IL4R). In the presence of IL4 only functional Type II IL4Rs were identified in normal or OA chondrocytes. With the exception of STAT2, no differences in JAK/STAT expression were detected between normal and OA cartilage. STAT2 was expressed in OA but not normal chondrocytes. Mechanical stimulation (MS) resulted in an IL4R-dependent increase in phosphorylated Tyk2 in normal chondrocytes, which could be abolished by IL1β preincubation. No phosphorylation of STAT5 or STAT6 was detected in either normal or OA chondrocytes following mechanical stimulation (MS) IL4 stimulation resulted in a decrease in Tyk2 phosphorylation and an increase in phosphorylation of STAT6 in both normal and OA chondrocytes.ConclusionChondrocytes from normal and OA cartilage signal through a Type II IL4R. This signalling is via a STAT6-independent pathway. Differences in IL4 signalling are likely due to crosstalk between integrin and cytokine signalling pathways, and not differences in IL4R expression