Update on the immunobiology of Sjögren's syndrome

B7-H4 deficiency in salivary gland of patients with primary Sjögren's syndrome impairs the regulatory effect on T cells

AIM

Our previous study confirmed the defect of B7-H4 expression in peripheral blood and salivary glands of patients with primary Sjögren's syndrome (pSS). The aim of this study was to analyze the effect of the deficit expression of B7-H4 on CD4⁺ T cells.

METHODS

CD4⁺ T cells were purified by magnetic-activated cell sorting MACS. The proliferation and cytokine production of CD4⁺ T cells co-cultured with purified salivary gland epithelial cells (SGECs) from pSS or non-SS sicca syndrome were detected.

RESULTS

By co-culturing the gland cells with CD4⁺ T cells, we found the proliferation of CD4⁺ T cells was significantly suppressed. The effect was weaker when SGECs from pSS patients were used compared to that from non-pSS sicca syndrome controls. Simultaneously, the productions of cytokines interleukin (IL)-5, IL-13, IL-17A, IL-6 in supernatant were reduced and also SGECs from pSS patients decreased them less than that from non-SS controls.

CONCLUSIONS

The decrease of B7-H4 expression in salivary glands of SS patients contributes to the defect of negatively regulating the inflammation caused by CD4⁺ T cells, thereby providing new insights into the role of B7-H4 in the inflammatory process of salivary glands in SS.

Sjögren's Syndrome Complicated by Myeloid/Natural Killer Cell Precursor Acute Leukemia: Case Report and Review of the Literature

We report a case of Sjögren's syndrome (SS) complicated by myeloid/natural killer (NK) cell precursor acute leukemia (M/NKPAL). A 75-year-old woman with a previous SS history for 2 years was routinely treated. Peripheral blood progenitor cells were increased, and subsequent bone marrow cell morphology examination showed the presence of acute myeloid leukemia type M4. However, flow cytometry analysis revealed that CD7/CD56/CD33/CD34/HLA-DR/cCD3 were all positive and myeloperoxidase- (MPO-) specific staining, other T cells, NK cells, and myeloid markers were all negative. Clonal T-cell receptor (TCR)β/TCRγ/TCRδ gene rearrangements and Epstein-Barr virus (EBV) were negative. The diagnosis of M/NKPAL was therefore confirmed. Unfortunately, this patient did not receive chemotherapy and later died of acute left heart failure and respiratory failure. SS complication with M/NKPAL is relatively rare. Combined with the relevant literatures, our study offers new insights into the clinical characteristics, pathological features, possible pathogenesis, and differential diagnosis of this rare disease.

TLR2 signals via NF-κB to drive IL-15 production in salivary gland epithelial cells derived from patients with primary Sjögren's syndrome

Toll-like receptors (TLRs) are pattern recognition receptors linking innate and adaptive immune responses, which resulted overexpressed in primary Sjögren's syndrome (pSS). Interleukin-15 (IL-15) is a pro-inflammatory cytokine which was recently demonstrated to be involved in pSS pathogenesis. The study was undertaken to clarify whether TLR2 is involved in the production of IL-15 in human salivary gland epithelial cells (SGEC) from pSS patients. SGEC primary cell cultures were established from pSS minor salivary gland tissues explanted from patients with a sure diagnosis of SS. After neutralization of TLR2 with a blocking monoclonal antibody, IL-15 production was assayed by immunoblotting and flow cytometry, IL-15 in the culture supernatants was measured by ELISA, and mRNA levels were assessed by RT-PCR and real-time PCR. The production of IL-15 by pSS SGEC decreased in culture supernatants and in protein lysates (p < 0.01) when TLR2 signaling was inhibited in pSS SGEC. In addition, a control at the transcriptional level was also detected; in fact, inhibition of nuclear factor (NF)-κB through the transfection of pSS SGEC with the dominant-negative inhibitory κBα proteins (IκBα) vector (IκBαDN) abrogated the stimulatory effect of TLR2 on IL-15 production. These data suggest that TLR2 activation is involved in the induction of IL-15 production by pSS SGEC and promotes inflammation through NF-κB activation. Therefore, therapeutic strategies that target TLR2/IL-15 pathway might be strong candidates for preventing or treating pSS.

Cytokine-induced STAT1 activation is increased in patients with primary Sjögren's syndrome

Limited data are available regarding the intracellular responses to different cytokines in primary Sjögren's syndrome (pSS). We studied the signal transducer and activator of transcription (STAT) activation profile in response to cytokine stimulations in peripheral blood mononuclear cells (PBMCs) from pSS patients by multicolor flow cytometry. The expression of the suppressors of cytokine signaling (SOCS), and interferon (IFN)-γ target genes in PBMCs was studied using quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). The induction of STAT1 phosphorylation in response to stimulation with IFN-α, IFN-γ or interleukin (IL)-6 was significantly increased in B cells and monocytes from pSS patients. Accordingly, the STAT1-mediated gene responses were significantly enhanced in PBMCs from pSS patients. Finally, the expression of SOCS1 and SOCS3 mRNA was increased in pSS patients. The results indicate increased sensitivity of immune cells from pSS patients to STAT1-activating signals, and may partly explain the IFN signature observed in pSS.

Interleukin (IL)-17-producing pathogenic T lymphocytes co-express CD20 and are depleted by rituximab in primary Sjögren's syndrome: a pilot study

Compelling evidence suggests that interleukin (IL)-17 and IL-17-producing cells play a pivotal role in the pathogenesis of primary Sjögren's syndrome (pSS). We investigated phenotypical and functional effects of the anti-CD20 antibody rituximab (RTX) on circulating and glandular IL-17-producing T cells in pSS. RTX is able to deplete glandular IL-17(+) CD3(+) CD4(-) CD8(-) double-negative (DN) and CD4(+) Th17 cells as well as circulating IL-17(+) DN T cells. A fraction of glandular and circulating IL-17(+) DN cells and CD4(+) T helper type 17 (Th17) cells co-expresses CD20 on the cell surface explaining, at least in part, such depletive capacity of RTX. The exposure to RTX does not rescue the in-vitro corticosteroid resistance of IL-17(+) DN T cells. Our results support further the therapeutic role in pSS of RTX that, despite its B cell specificity, appears able to also hamper IL-17-producing T cells in this disease.

Mobilization of lymphatic endothelial precursor cells and lymphatic neovascularization in primary Sjögren's syndrome

Although lymphatic neovascularization may be a key feature of chronic inflammation, it is almost unexplored in primary Sjögren's syndrome (pSS). A recent study revealed a pro‐lymphangiogenic function of interleukin (IL)‐17, a leading player in pSS pathogenesis. The aims of the study were to investigate lymphangiogenic mediators and lymphatic vasculature in pSS, as well as their possible association with IL‐17. Circulating lymphatic endothelial precursor cells (LEPCs) and Th17 cells were enumerated in pSS patients and healthy donors. VEGF‐C and IL‐17 levels were assessed in paired serum samples. Lymphatic vasculature, VEGF‐C/VEGF receptor (VEGFR)‐3 and IL‐17 were evaluated in pSS minor salivary glands (MSGs) and compared with normal and non‐specific chronic sialadenitis (NSCS) MSGs. Circulating LEPCs were expanded in pSS and correlated with circulating Th17 cells, IL‐17 and VEGF‐C. In pSS MSGs, a newly formed lymphatic capillary network was found within periductal inflammatory infiltrates and the number of interlobular lymphatic vessels was significantly increased compared with normal and NSCS MSGs. Strong VEGF‐C expression was detected in pSS ductal epithelial cells and periductal inflammatory cells. Numerous VEGFR‐3⁺ infiltrating mononuclear cells were exclusively observed in pSS MSGs. VEGFR‐3 expression was strongly increased in lymphatic capillaries of pSS MSGs. IL‐17⁺ inflammatory cells were preferentially observed around lymphatic vessels in pSS MSGs. This study supports the notion that lymphvasculogenesis and lymphangiogenesis are active in pSS, thereby unmasking a novel aspect of disease pathogenesis. In addition, our results suggest another possible pathogenic role of IL‐17 in pSS, further supporting its therapeutic targeting in this disease.

HTLV-1, Immune Response and Autoimmunity

Human T-lymphotropic virus type-1 (HTLV-1) infection is associated with adult T-cell leukemia/lymphoma (ATL). Tropical spastic paraparesis/HTLV-1-associated myelopathy (PET/HAM) is involved in the development of autoimmune diseases including Rheumatoid Arthritis (RA), Systemic Lupus Erythematosus (SLE), and Sjögren's Syndrome (SS). The development of HTLV-1-driven autoimmunity is hypothesized to rely on molecular mimicry, because virus-like particles can trigger an inflammatory response. However, HTLV-1 modifies the behavior of CD4⁺ T cells on infection and alters their cytokine production. A previous study showed that in patients infected with HTLV-1, the activity of regulatory CD4⁺ T cells and their consequent expression of inflammatory and anti-inflammatory cytokines are altered. In this review, we discuss the mechanisms underlying changes in cytokine release leading to the loss of tolerance and development of autoimmunity.