Prion diseases are transmissible and result in fatal neurode

Prion diseases are transmissible and result in fatal neurodegenerative disorders, which, similar to AD, also involve the infiltration and activation of mononuclear phagocytes in Protease Inhibitor Library lesions (reviewed in [61]). A 21 amino-acid fragment of the aberrant human prion protein, Prp106–126, can form fibrils in vitro and elicits a diverse array of inflammatory responses by mononuclear phagocytes [61]. This prion-peptide fragment activates FPRL1 to induce human monocyte migration and to increase the production of the proinflammatory cytokines tumor necrosis factor (TNF)-α and IL-1β; both of which are implicated as neurotoxic mediators [54]. Thus, FPRL1 might also participate in inflammatory pathology seen in prion diseases.
Future perspectives For ∼25 years, speculation about the biological roles of the high affinity FPR was limited primarily to anti-bacterial host defense. Although this view has been supported by studies in FPR1−/− mice, it is not yet clear how general the activity is. Moreover, the discovery of novel related receptors, non-formylated peptide and lipid agonists for these receptors, and their expression in diverse tissues and cell types, indicates that this receptor family could have diverse and complex roles in biology. The most important task facing future work in this area is to determine whether these new ligand–receptor interactions actually occur under physiologic or pathophysiologic conditions in vivo and what the consequences are. The identification of functional agonists for human FPRL2 and its persistent expression during myeloid DC maturation [20] prompt more in depth studies of this receptor in pathophysiology. Additional research should also determine the significance of FPR and FPRL1 expression on non-hematopoietic cells. Several of these cells respond functionally to receptor agonists in vitro. For example, hepatocytes respond to fMLF by producing acute-phase proteins [62], astrocytoma cells express both FPR and FPRL1 and are activated by agonists to migrate and release proinflammatory cytokines [63], and also, fMLF can induce blood vessel contraction [64]. This response could be direct or indirect because FPR and FPRL1 are expressed not only on mononuclear cells, which might infiltrate the intima, but also on endothelial cells and smooth muscle cells [64]. Also, future research will need to address the perplexing issue of how the same receptor can bind such structurally diverse ligands, ranging from small peptides to large proteins to lipids in the case of FPRL1. The peptides do not have significant primary or known tertiary structure similarities. Moreover, many of these novel ligands are active only at concentrations in the micromolar range, which raises questions about their quaternary structural state. This is particularly important for amyloidogenic peptides, which form fibrils. Such studies will help identify whether the various ligands bind by shared or unique domains, an important consideration for the development of antagonists. In this context, although annexin I peptides and LXA4 elicit both pro- and anti-inflammatory signals through their respective receptors, FPR and FPRL1, respectively, spinorphin (LVVYPWT) acts as an endogenous antagonist of FPR [11]. This discovery identifies a direct mechanism by which FPR ligands might negatively regulate inflammatory responses and suggests that the development of drugs to block FPRs could be both useful and possible.
Acknowledgements
Introduction Rheumatoid arthritis (RA) is a common chronic autoimmune disease, characterized by joint inflammation, synovial hyperplasia and progressive joint destruction. The pathogenesis of RA involves the interaction of multiple cell types including leukocytes such as neutrophils, macrophages and lymphocytes, and the local fibroblast-like synoviocytes (FLS). CD4 T cells play a critical role in the development of RA, both as drivers of the adaptive immune response and effectors of injury, with regulatory foxp3+ CD4 T cells (Tregs) being protective [[1], [2], [3], [4]]. B cells and autoantibodies also play an important role in RA [5,6].