**8. Summary**

66 Rheumatoid Arthritis – Etiology, Consequences and Co-Morbidities

Low density granulocytes (LDG) are present in PBMC preparations derived from lupus patients. LDGs display an activated phenotype, induce significant endothelial cytotoxicity and synthesize sufficient levels of type I IFNs to disrupt the capacity of endothelial

EPCs have been shown to play a role in the neovascularization that occurs in diseased tissues. Given the extensive neovascularization that occurs in RA, it was suggested by Denny (Denny et al., 2010) that EPCs are recruited to the arthritic synovium, where they might contribute to expansion of the synovial microcirculation. The VCAM-1/very late activation antigen 4 adhesive system critically mediated EPC adhesion to cultured RA fibroblasts. As was shown, in 3 diverse animal models used to investigate cell homing in arthritis, EPCs preferentially localized to inflamed synovium compared to normal synovium (Silverman et al., 2007). This correlates well with earlier observations that the number of EPCs per mm2 identified immunihistochemically in postsurgical human RA synovial tissue (ST) was elevated ~25-fold

The findings provide evidence of a possible role of EPC in the synovial neovascularization that is critical to RA pathogenesis; and it may be suggested that neutrophils play a crucial role in this phenomenon. As was showed by Schruefer (Schruefer et al., 2004), neutrophils are critically involved in angiogenesis. Growing evidences indicates that angiogenesis can be initiated by inflammatory cytokines, including IL-8. Human neutrophils release a variety of proinflamatory cytokines, including IL-8, which was originally identified as a potent activator of human neutrophils (Baggiolini et al., 1989). Subsequently, IL-8 was shown to stimulate angiogenesis by promoting proliferation of endothelial cells, moreover IL-8 inhibits endothelial cell apoptosis and induces the upregulation of endothelial matrix

Neovascularization is a hallmark of diverse pathological conditions, including RA. Microcirculatory expansion occurs either through angiogenesis (the proliferation and branching off of pre-existing microvessels, by IL-8 from neutrophils), or by vasculogenesis (the de novo formation of blood vessels from circulating EPCs). This phenomenon may be

Inhibition of neovascularization and thus inhibition of the expansion of invasive tissue in RA is the desired effect. A clearer understanding of the role of neutrophils in biologic processes that guide EPCs to the angiogenic tissue and exert contradictory effects on mirocirculatory expansion may lead to the development of the novel tools to modulate these

**7. Neutrophil-mediated monocyte recruitment. View on neutrophil-monocyte** 

The sequence of phagocyte recruitment to the site of inflammation comprises initial extravasation of neutrophils followed by a subsequent emigration of monocytes. The experiments of Gallin (Gallin et al., 1982) pointed to the importance of ready made neutrophil granule proteins in the recruitment of monocytes. Granule proteins are stored in 4 distinct sets of granules. Primary and secondary granules discharged from emigrated neutrophils contain mainly antimicrobial polypeptides. Rapidly mobilized secretory vesicles contain mainly receptors important for adhesion and recognition of foreign particles. Tertiary granules released during transendothelial migration contain mainly proteases

progenitor cells (EPC) to differentiate into mature endothelial cells.

over the number of EPCs localized in normal ST (Ruger et al., 2004).

restored by LDG depletion (Denny et al., 2010).

activities (Silverman et a., 2007).

(Soehlein et al., 2009).

**axis** 

metalloproteinase-2 and -9, which also play an important role in angiogenesis.

The research conditions of most neutrophil experiments differ considerably from the physiological environment of the joint, i.e. the presence and concentration of cytokines such as TNF-α, IL-1β, IL-6, IL-8, IL-12, IL-17, IL-18, IL-23 and IFN-γ (McInnes et al., 2007), and physical factors such as viscosity, oxygen concentration, and pressure. Each of these differences can influence neutrophil metabolism and activation (Gajewski et al., 2006, 2010a; Cross et al., 2006). Reasoning that conditions imitating physiological environment are required for proper conclusions, we developed and used culture systems which more accurately simulated conditions in the joint (Gajewski, et al., 2010b). The proposal to

The Role of Neutrophils in Rheumatoid Arthritis – Experiments *In Vitro*: A Change of Conception? 69

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Findings confirm that neutrophils in synovial tissues have different features than blood neutrophils. The old view of neutrophils as a terminally differentiated cell completely focused on destroying pathogens and tissues is no longer held (Cascao et al., 2009). Our understanding of the role of neutrophils in inflammation has changed fundamentally over recent years. The initial perception of the neutrophil playing a passive role and merely responding to external signals has now been replaced by an appreciation that activated neutrophils can perform most, if not all, the functions of macrophages (Cascao et al., 2009).

Neutrophils are key cells in the immune response due to their dual anti-infection and proinflammatory roles, being critical effectors in both innate and humoral immunity. Neutrophils generate chemotactic signals and cytokines that recruit, differentiate and activate B and T lymphocytes and antigen presentating cells (APCs), thus establishing a "bridge" between the innate and adaptive immune system. Neutrophils seem to be important "decision-shapers" (Cascao et al., 2009) in this complex system and further understanding of the specific roles of these cells may help to answer one of the main questions in the immune system domain; "What triggers an immune response?" (Cascao et al., 2009).

The knowledge about neutrophil complex biology and their role in immune-mediated inflammatory diseases is expected to reveal promising new therapeutic targets.

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**5** 

*Japan* 

**Molecular Mechanisms of Rheumatoid Arthritis** 

The immune system is a highly organized defense system, which recognizes invading microorganisms and aims to exclude them. In order to do this effectively and safely, the immune system must distinguish between self- and non-self-antigens, and be tolerant of self-antigens. Autoimmune diseases develop through the breakdown of self-tolerance, as a result of immune deregulation. This is caused by the combined influence of genetic and environmental factors, including infectious microorganisms. Rheumatoid arthritis (RA) is a systemic autoimmune disease, characterized by synovial hyperplasia leading to the destruction of bones and joints. This severely impairs the life of patients. RA is a relatively common autoimmune disease, occurring in approximately 1% of the population. However, its etiology and pathophysiology are not completely understood. The incidence of RA is correlated with certain human leukocyte antigen (HLA)-DR haplotypes, and the production of autoantibodies such as rheumatoid factor and anticitrullinated protein autoantibody. Thus, the involvement of the deregulated immune system is strongly implicated. Various molecules, including type II collagen, gp39, citrullinated peptides, and glucose-6 phosphoisomerase, have been reported as potential pathogenic autoantigens. However, their involvement explains only a proportion of RA cases. Autoantigens are abundant in the body and, theoretically, the immune response to them continues indefinitely. Thus, systemic

In the pathological condition of RA, the joints are infiltrated with T cells, B cells, macrophages, and plasma cells, all of which are characteristic chronic inflammation cells driven by the immune system. Recently, Th17, a novel helper T-cell subset producing interleukin (IL)-17, has been recognized as a pivotal player in the local inflammation driven by acquired immunity. In addition to immune-competent cells, there is accumulating evidence for abnormalities in non-hematopoietic cells, especially fibroblast-like synoviocytes (FLSs) (Bartok & Firestein, 2010; Firestein, 2009; Mor *et al.*, 2005; Pap & Gay, 2009). The cartilage and bone are destroyed by the invasion of pannus, which is formed from proliferating FLSs and multi-nucleated osteoclasts. Osteoclasts are specialized to resolve bone, and play a major role in bone destruction in RA. However, there is strong evidence that FLSs themselves are aggressive enough to destroy bone. When cultured FLSs derived from RA or osteoarthritis (OA) were co-implanted with human cartilage under the renal

autoimmune diseases exhibit the characteristics of chronic inflammation.

**1. Introduction** 

**Revealed by Categorizing Subtypes of** 

**Fibroblast-Like Synoviocytes** 

Katsuhiko Ishihara and Hideya Igarashi

*Kawasaki Medical School* 

