Increased concentrations of DNA-containing immune complexes in the serum are associated with systemic autoimmune diseases such as lupus. Stimulation of Toll-like receptor 9 (TLR9) by DNA is important in the activation of plasmacytoid dendritic cells and B cells. Here we show that HMGB1, a nuclear DNA-binding protein released from necrotic cells, was an essential component of DNA-containing immune complexes that stimulated cytokine production through a TLR9-MyD88 pathway involving the multivalent receptor RAGE. Moreover, binding of HMGB1 to class A CpG oligodeoxynucleotides considerably augmented cytokine production by means of TLR9 and RAGE. Our data demonstrate a mechanism by which HMGB1 and RAGE activate plasmacytoid dendritic cells and B cells in response to DNA and contribute to autoimmune pathogenesis.

Prostaglandin (PG)E2 is a potent mediator of pain and inflammation, and high levels of this lipid mediator are observed in numerous disease states. The inhibition of PGE2 production to control pain and to treat diseases such as rheumatoid arthritis to date has depended on nonsteroidal antiinflammatory agents such as aspirin. However, these agents inhibit the synthesis of all prostanoids. To produce biologically active PGE2, PGE synthases catalyze the isomerization of PGH2 into PGE2. Recently, several PGE synthases have been identified and cloned, but their role in inflammation is not clear. To study the physiological role of the individual PGE synthases, we have generated by targeted homologous recombination a mouse line deficient in microsomal PGE synthase 1 (mPGES1) on the inbred DBA͞1lacJ background. mPGES1-deficient (mPGES1 ؊/؊ ) mice are viable and fertile and develop normally compared with wild-type controls. However, mPGES1 ؊/؊ mice displayed a marked reduction in inflammatory responses compared with mPGES1 ؉/؉ mice in multiple assays. Here, we identify mPGES1 as the PGE synthase that contributes to the pathogenesis of collagen-induced arthritis, a disease model of human rheumatoid arthritis. We also show that mPGES1 is responsible for the production of PGE 2 that mediates acute pain during an inflammatory response. These findings suggest that mPGES1 provides a target for the treatment of inflammatory diseases and pain associated with inflammatory states.arthritis ͉ inflammation ͉ macrophage ͉ knockout ͉ PGE2

When challenged with extracellular ATP, leukocytes respond and activate processes attributed to the P2X7 receptor (P2X7R), an unusual ligand-gated ion channel. To prove P2X7R involvement, blood samples from P2X7R-deficient mice were characterized. Monocytes and lymphocytes associated with wild-type blood responded to ATP and underwent volume/shape changes and shed L-selectin. In contrast, leukocytes from P2X7R-deficient animals demonstrated no change in physical properties or L-selectin expression following ATP challenge. Blood stimulated with LPS or ATP individually generated minimal quantities of the leaderless polypeptide IL-1β, but sequential treatment of wild-type, but not P2X7R-deficient, blood with LPS and ATP yielded large amounts of cell-free cytokine. Based on these differences, wild-type and P2X7R-deficient animals were compared following induction of monoclonal anti-collagen-induced arthritis. Ab-treated wild-type animals subsequently challenged with LPS developed inflamed, swollen paws; their joint cartilage demonstrated lesions, loss of proteoglycan content, and the presence of collagen degradation products. P2X7R-deficient animals subjected to the same challenge were markedly less affected; both the incidence and severity of disease were reduced. These data indicate that ATP does act via the P2X7R to affect leukocyte function and that the P2X7R can serve as an important component of an in vivo inflammatory response.

Platelet activation is characterized by shape change, induction of fibrinogen receptor expression and release of granular contents, leading to aggregation and plug formation. While this response is essential for hemostasis, it is also important in the pathogenesis of a broad spectrum of diseases, including myocardial infarction, stroke and unstable angina. Adenosine 5'-diphosphate (ADP) induces platelet aggregation, but the mechanism for this has not been established, and the relative contribution of ADP in hemostasis and the development of arterial thrombosis is poorly understood. We show here that the purinoceptor P2Y1 is required for platelet shape change in response to ADP and is also a principal receptor mediating ADP-induced platelet aggregation. Activation of P2Y1 resulted in increased intracellular calcium but no alteration in cyclic adenosine monophosphate (cAMP) levels. P2Y1-deficient platelets partially aggregated at higher ADP concentrations, and the lack of P2Y1 did not alter the ability of ADP to inhibit cAMP, indicating that platelets express at least one additional ADP receptor. In vivo, the lack of P2Y1 expression increased bleeding time and protected from collagen- and ADP-induced thromboembolism. These findings support the hypothesis that the ATP receptor P2Y1 is a principal receptor mediating both physiologic and pathological ADP-induced processes in platelets.