[Rheumatoid arthritis: new molecular and cellular aspects]

Differences of IL-1β Receptors Expression by Immunocompetent Cells Subsets in Rheumatoid Arthritis

IL-1β is involved in the induction and maintenance of chronic inflammation in rheumatoid arthritis (RA). Its activity is regulated and induced by soluble and membrane-bound receptors, respectively. The effectiveness of the cytokine depends not only on the percentage of receptor-positive cells in an immunocompetent subset but also on the density of receptor expression. The objective of this study was to investigate the expression of IL-1β membrane-bound receptors (IL-1R1 and IL-1R2) in terms of the percentage of receptor-positive cells and the number of receptors per cell in different subsets of immune cells in RA patients before and after a course of basic (excluding anticytokine) therapy and in healthy individuals. The resulting data indicate differences in the expression of IL-1β receptors among T cells, B cells, and monocytes in healthy volunteers and in rheumatoid arthritis patients. The importance of determining both the relative percentage of cells expressing receptors to immunomodulatory cytokines and the number of membrane-bound receptors per cell is highlighted by evidence of unidirectional or multidirectional changing of these parameters according to cell subset and health status.

Hypoxia. Regulation of NFkappaB signalling during inflammation: the role of hydroxylases

NFκB is a master regulator of innate immunity and inflammatory signalling. Microenvironmental hypoxia has long been identified as being coincident with chronic inflammation. The contribution of microenvironmental hypoxia to NFκB-induced inflammation has more recently been appreciated. Identification of the co-regulation of NFκB and hypoxia inducible factor (HIF) pathways by 2-oxo-glutarate-dependent hydroxylase family members has highlighted an intimate relationship between NFκB inflammatory signalling and HIF-mediated hypoxic signalling pathways. Adding another layer of complexity to our understanding of the role of NFκB inflammatory signalling by hypoxia is the recent recognition of the contribution of basal NFκB activity to HIF-1α transcription. This observation implicates an important and previously unappreciated role for NFκB in inflammatory disease where HIF-1α is activated. The present review will discuss recent literature pertaining to the regulation of NFκB inflammatory signalling by hypoxia and some of the inflammatory diseases where this may play an important role. Furthermore, we will discuss the potential for prolylhydroxylase inhibitors in inflammatory disease.

[Pathogenesis of osteoporosis in rheumatoid arthritis]

Osteoporosis is a major clinical problem in rheumatoid arthritis. Patients with rheumatoid arthritis frequently not only present with juxta articular osteopenia and bone erosions but also with generalized axial and appendicular osteoporosis at sites distant from inflamed joints. The pathogenesis of bone loss in rheumatoid arthritis is multifactorial; disease activity certainly is a major determinant of bone mass. Further pathogenetic factors include effects of anti-inflammatory therapies (in particular glucocorticoids), reduced mobility, estrogen and/or androgen deficiency. Recently, receptor activator of nuclear factor kappa B ligand (RANKL) and osteoprotegerin (OPG), a decoy receptor for receptor activator of nuclear factor kappa B ligand, were identified as central regulators of osteoclast recruitment and activation. Osteoprotegerin and receptor activator of nuclear factor kappa B ligand production is modulated by several cytokines, growth factors and hormones. In rheumatoid synovium both fibroblasts and activated T cells express receptor activator of nuclear factor kappa B ligand and thereby promote osteoclast recruitment and activation. Thus, osteoprotegerin and receptor activator of nuclear factor kappa B ligand appear to represent important molecular links between the immune system and bone metabolism in rheumatoid arthritis.

Effects of synovial fluid on the respiratory burst of granulocytes in rheumatoid arthritis

Neutrophil infiltration in the synovia is an important feature of the local inflammatory process associated with rheumatoid arthritis. The present study is focused on the effects exerted in vitro by the synovial fluid versus serum on the respiratory burst of granulocytes isolated either from blood or synovial fluid of rheumatoid arthritis patients. The respiratory burst was evaluated as superoxide anion release, by lucigenin-amplified chemiluminescence. Our data show that the respiratory burst of granulocytes isolated from rheumatoid arthritis patients might trigger a significant oxidative stress both in periphery and the inflamed joint. These cells show no pathological pattern when activated in vitro by the chemotactic peptide fMLP, heterologous synovial fluid or serum. Acellular synovial fluid amplifies the superoxide anion release induced by fMLP more than the corresponding serum, indicating that a bacterial infection in the joint might enhance the oxidative damage in the inflamed synovium.