Heparan sulfate regulates IL-21 bioavailability and signal strength that control germinal center B cell selection and differentiation.

In antibody responses, mutated germinal center B (BGC) cells are positively selected for reentry or differentiation. As the products from GCs, memory B cells and antibody-secreting cells (ASCs) support high-affinity and long-lasting immunity. Positive selection of BGC cells is controlled by signals received through the B cell receptor (BCR) and follicular helper T (TFH) cell-derived signals, in particular costimulation through CD40. Here, we demonstrate that the TFH cell effector cytokine interleukin-21 (IL-21) joins BCR and CD40 in supporting BGC selection and reveal that strong IL-21 signaling prioritizes ASC differentiation in vivo. BGC cells, compared with non-BGC cells, show significantly reduced IL-21 binding and attenuated signaling, which is mediated by low cellular heparan sulfate (HS) sulfation. Mechanistically, N-deacetylase and N-sulfotransferase 1 (Ndst1)-mediated N-sulfation of HS in B cells promotes IL-21 binding and signal strength. Ndst1 is down-regulated in BGC cells and up-regulated in ASC precursors, suggesting selective desensitization to IL-21 in BGC cells. Thus, specialized biochemical regulation of IL-21 bioavailability and signal strength sets a balance between the stringency and efficiency of GC selection.

Supranutritional selenium suppresses ROS-induced generation of RANKL-expressing osteoclastogenic CD4+ T cells and ameliorates rheumatoid arthritis.

OBJECTIVE: The benefit of Se supplementation in rheumatoid arthritis (RA) has been tested in clinical trials, but results remain inconclusive. The objective of this study was to specifically investigate the potential benefit of supranutritional Se by examining human samples from an area with supranutritional Se intake and testing a mouse model of RA. METHODS: Peripheral blood mononuclear cells (PBMCs) from RA patients (N = 57) and healthy controls (HC, N = 71) from an area of supranutritional Se intake (Enshi, Hubei, China) were analysed by flow cytometry. Serum cytokine and Se levels were measured by cytometric beads array (CBA) and inductively coupled plasma mass spectrometry (ICP-MS), respectively. With sufficient or supranutritional selenium intake, mice were induced with collagen-induced arthritis (CIA) and examined for disease activity and immunopathology. The influence of Se supplementation in the generation of RANKL-expressing osteoclastogenic CD4+ T cells was investigated by in vitro assays. RESULTS: In Enshi city, HC showed the above-normal concentrations of serum Se concentrations while RA patients were enriched in the normal range (70-150 ng mL-1) or below. RA patients with higher Se levels demonstrated milder disease and lower levels of C-reactive protein, IL-6, RANKL and Th17 cells. In the mouse CIA model, supranutritional Se supplementation delayed disease onset, ameliorated joint pathology and reduced CD4+CD44+RANKL+ T cells. Se supplementation could suppress RANKL expression in cultured mouse Th17 cells. CONCLUSION: Supranutritional Se suppresses RANKL-expressing osteoclastogenic CD4+ T cells and could be beneficial to RA, which warrants formal testing in randomised clinical trials.

Sustained low-dose interleukin-2 therapy alleviates pathogenic humoral immunity via elevating the Tfr/Tfh ratio in lupus.

OBJECTIVES: Low-dose interleukin-2 (IL-2) has shown promising clinical benefits in the treatment of systemic lupus erythematosus (SLE), but how this therapy alleviates pathogenic humoral immunity remains not well understood. The dilemma is that IL-2 can suppress both follicular helper and regulatory T (Tfh and Tfr) cells, which counteract each other in regulating autoantibody production. METHODS: Female NZB/W F1 mice received recombinant human IL-2 (3 × 104 IU/dose) in three treatment regimens: (1) short, daily for 7 days; (2) medium, daily for 14 days, and (3) long, every second day for 28 days. Tfh (Foxp3-CXCR5+Bcl6+), Tfr (Foxp3+CXCR5+Bcl6+), germinal centre (GC, B220+GL-7+Fas+) and antibody-secreting cell (ASC, B220-CD138+TACI+) were analysed by flow cytometry. Serum anti-dsDNA level was determined by ELISA. Kidney pathology was evaluated by H&E and immunofluorescence staining. Circulating Tfh and Tfr cells in SLE patients treated with low-dose IL-2 from a previous clinical trial (NCT02084238) was analysed. RESULTS: Low-dose IL-2 treatment consistently increased Tfr/Tfh ratio in mice and SLE patients, because of a stronger suppression on Tfh cells than Tfr cells. Three treatment regimens revealed distinct immunological features. Tfh suppression was observed in all regimens, but Tfr suppression and GC reduction were recorded in just medium and long regimens. Only the long treatment regimen resulted in inhibited ASC differentiation in spleen, which was accompanied by reduced anti-dsDNA titres and ameliorated kidney pathology. CONCLUSION: Low-dose IL-2 therapy increases the Tfr/Tfh ratio, and a less frequent and prolonged treatment can alleviate pathogenic humoral immunity and improve renal function.