Regulation of peripheral blood and synovial fluid lymphocyte apoptosis in juvenile idiopathic arthritis

Juvenile idiopathic arthritis and physical activity: possible inflammatory and immune modulation and tracks for interventions in young populations

Juvenile idiopathic arthritis (JIA) is a chronic inflammatory disease characterized by persistent joint inflammation that manifests as joint pain and swelling and limited range of joint motion. In healthy subjects, the literature reports that physical activity has an anti-inflammatory effect. In JIA patients, exercise could be used as a therapeutic tool to counteract disease-related inflammation and thereby improve clinical symptoms, although transient flare of pain could be the price to pay. Indeed, in patients with a chronic inflammatory disease, physical activity is prone to exacerbate underlying inflammatory stress. Physical activity improves quality of life and symptoms in JIA patients, but the mechanisms of action remain unclear. This review focuses on the mechanisms underlying exercise-induced immune and hormonal changes. Data on the impact of acute and chronic physical activities on the secretion of hormones and other molecules such as miRNA or peptides involved in the inflammatory process in JIA was compiled and summarized, and the key role of the biological effect of muscle-derived interleukin 6 in the exercise-induced modulation of pro/anti-inflammatory balance is addressed. We also go on to review the effect of training and type of exercise on cytokine response. This review highlights the beneficial effect of physical exercise in children with JIA and potential effect of exercise on the balance between pro- and anti-inflammatory response.

Monocytes are resistant to apoptosis in systemic juvenile idiopathic arthritis

We investigated whether circulating monocytes from patients with systemic juvenile idiopathic arthritis (SJIA) are resistant to apoptosis and which apoptotic pathway(s) may mediate this resistance. A microarray analysis of peripheral blood mononuclear cells (PBMC) of SJIA samples and RT-PCR analysis of isolated monocytes showed that monocytes from active SJIA patients express transcripts that imply resistance to apoptosis. SJIA monocytes incubated in low serum show reduced annexin binding and diminished FasL up-regulation compared to controls. SJIA monocytes are less susceptible to anti-Fas-induced apoptosis and, upon activation of the mitochondrial pathway with staurosporine, show diminished Bid cleavage and Bcl-w down-regulation compared to controls. Exposure to SJIA plasma reduces responses to apoptotic triggers in normal monocytes. Thus, SJIA monocytes are resistant to apoptosis due to alterations in both the extrinsic and intrinsic apoptosis pathways, and circulating factors associated with active SJIA may confer this phenotype.

Oligoarticular and polyarticular JIA: epidemiology and pathogenesis

Juvenile idiopathic arthritis (JIA) refers to a group of chronic childhood arthropathies of unknown etiology, currently classified into subtypes primarily on the basis of clinical features. Research has focused on the hypothesis that these subtypes arise through distinct etiologic pathways. In this Review, we discuss four subtypes of JIA: persistent oligoarticular, extended oligoarticular, rheumatoid-factor-positive polyarticular and rheumatoid-factor-negative polyarticular. These subtypes differ in prevalence between ethnic groups and are associated with different HLA alleles. Non-HLA genetic risk factors have also been identified, some of which reveal further molecular differences between these subtypes, while others suggest mechanistic overlap. Investigations of immunophenotypes also provide insights into subtype differences: adaptive immunity seems to have a prominent role in both polyarticular and oligoarticular JIA, and the more-limited arthritis observed in persistent oligoarticular JIA as compared with extended oligoarticular JIA may reflect more-potent immunoregulatory T-cell activity in the former. Tumor necrosis factor seems to be a key mediator of both polyarticular and oligoarticular JIA, especially in the extended oligoarticular subtype, although elevated levels of other cytokines are also observed. Limited data on monocytes, dendritic cells, B cells, natural killer T cells and neutrophils suggest that the contributions of these cells differ across subtypes of JIA. Within each subtype, however, common pathways seem to drive joint damage.

Relationship between impaired apoptosis of lymphocytes and distribution of dendritic cells in peripheral blood and synovial fluid of children with juvenile idiopathic arthritis

Introduction:

The pathogenesis of juvenile idiopathic arthritis (JIA) is not fully understood. Recently the present authors described disturbed apoptosis of JIA lymphocytes in both peripheral blood (PB) and synovial fluid (SF) as well as an abnormal distribution of blood dendritic cells (BDCs) between the PB and SF in this disease. Possible relationships between these events during the development of JIA process are assessed here.

Materials and Methods:

Lymphocyte apoptosis and BDC counts were assessed in the PB and SF of untreated JIA children. Lymphocyte apoptosis was analyzed by the Annexin-V/propydium iodide assay. Total DC (TDC) number was based on the sum of three BDC subpopulations determined using a panel of monoclonal antibodies against BDC antigens (BDCA): myeloid type 1 (mDC1, BDCA-1⁺/HLA-DR⁺/CD19^-), myeloid type 2 (mDC2, BDCA-3⁺/HLA-DR⁺/CD14^-), and plasmacytoid (pDC, BDCA-2⁺/HLA-DR⁺/CD123⁺). Cells were enumerated by the flow cytometric “single-platform” method. The concentration of tumor necrosis factor (TNF)-α and the distribution of particular lymphocyte subtypes in both PB and SF were also investigated.

Results:

There was significant positive correlation between apoptosis of PB lymphocytes and SF TDC count (p=0.002) as well as SF TNF-α concentration (p=0.007). SF TNF-α levels also correlated with SF TDC count (p=0.003). Moreover, JIA SF was distinctly enriched with CD4+ and CD8+ T lymphocytes and included CD4⁺/CD25^high cells as well. There was significant positive correlation between the number of CD4⁺/CD25^high cells and SF JIA BDC count (p=0.015).

Conclusions:

These data suggest a possible link between impaired apoptosis of PB/SF lymphocytes and increased recruitment of PB BDCs to SF and other elements of the immune system in JIA, including regulatory CD4+/CD25high cells.

[Concepts on the pathogenesis of juvenile idiopathic arthritis]

There are various explanations for the development of juvenile idiopathic arthritis (JIA).Gene changes in the immune system can predispose to JIA and regulation of the immune system is crucial in the pathogenesis. The adaptive, acquired immune system probably plays a central role. Thus, in the case of JIA a conspicuous population of highly activated T-cells can be found in the synovia. B-cells are also involved, as indicated by positive ANA titers in JIA patients. Regulatory T-cells (Tregs) attempt to prevent the expansion of autoreactive T-cells.However, the natural or the innate immune system also plays a role. Thus a disorder of the inflammasome could underlie the cause of JIA with systemic onset. The interaction between congenital and adaptive immune system shows that a distinct spatial and temporal separation between the two immune systems is becoming increasingly difficult. An infection- and virus-related immune reaction could also be the cause of JIA. Proinflammatory cytokines are of proven significance in pathogenesis in terms of how they are released under stress, for example. New genomic and proteomic techniques are able to produce individualized profiles for each patient and allow for increasingly fine separation between subtypes, thus improving therapeutic possibilities.