In the enclosed study we have examined the expression and contribution of specific chemokines, macrophage inflammatory protein la (MIP-la) and macrophage inflammatory protein 2 (MIP-2), and interleukin 10 (IL-10) during the evolution of type II collagen-induced arthritis (CIA). Detectable levels of chemotactic cytokine protein for MIP-la and MIP-2 were first observed between days 32 and 36, after initial type II collagen challenge, while increases in IL-10 were found between days 36 and 44. CIA mice passively immunized with antibodies directed against either MIWP-la or MIP-2 demonstrated a delay in the onset of arthritis and a reduction of the severity of arthritis. On the contrary, CIA mice receiving neutralizing anti-IL-10 antibodies demonstrated an acceleration of the onset and an increase in the severity of arthritis. Interestingly, anti-IL-10 treatment increased the expression of MWP-la and MWP-2, as well as increased myeloperoxidase (MPO) activity and leukocyte infiltration in the inflamed joints. These data suggest that MWP-la and MWP-2 play a crucial role in the initiation and maintenance, while IL-10 appears to play a regulatory role during the development of experimental arthritis. (J. Clin. Invest. 1995. 95:2868-2876

Polymorphonuclear neutrophils (PMNs) are usually thought of as the leukocyte population involved in acute inflammatory responses, acting as a first line of defense against invading microorganisms. These terminally differentiated cells are generally not thought of as an important source of de novo synthesis of polypeptide mediators. Recent progress has shown, however, that PMNs are able to synthesize cytokines in response to a variety of inflammatory stimuli and during certain pathological conditions. The expression profiles of PMN-derived cytokines are similar with those of monocytes/macrophages, major professional phagocytes. Like monocytes, PMNs are able to secrete proinflammatory cytokines [e.g., tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta], both CC and CXC chemokines [e.g., IL-8, interferon-inducible protein 10 (IP-10) and macrophage inflammatory protein (MIP)-1alpha], and angiogenic factors [e.g., vascular endothelial growth factor (VEGF)]. The secretion of cytokines by activated PMNs is regulated by immunoregulatory cytokines such as interferon (IFN)-gamma, IL-4, IL-10 and IL-13. In addition to acute inflammatory responses, PMNs and PMN-derived cytokines appear to be involved in the pathogenesis of such chronic inflammatory disorders as rheumatoid arthritis, inflammatory bowel diseases and mycobacterial infections. Conceivably, these findings place PMNs at a pivotal position where they regulate and orchestrate not only acute inflammatory responses but also chronic inflammation and immune regulation. As such, inhibition of PMN-derived cytokines is viewed as a potentially useful strategy for therapeutic immunointervention.

Cell-mediated immunity is defined as a beneficial host response characterized by an expanded population of specific T cells, which, in the presence of antigens, produce cytokines locally. The activation and recruitment of cells into an area of inflammation is a crucial step in the development of DTH responses. DTH is immunologically a process similar to cell-mediated immunity, involving T cells and cytokines. CD4 T helper (Th) 1 cells, differentiated from naive Th cells by IL-12 and IL-18 produced from macrophages, play a regulatory role in the expression of DTH and activation of macrophages via interferon gamma generated by Th1 and natural killer cells. Macrophages accumulate at the site of DTH and become activated through the CD4 Th1 cell-cytokine-macrophage axis. However, DTH leads to pathologic responses, such as granulomatous inflammation, calcification, caseation necrosis, and cavity formation. Granulomas usually form as a result of the persistence of a nondegradable product or as the result of DTH responses. DTH is also required for host defense against etiologic agents, such as Mycobacterium tuberculosis. The expression of cell-mediated immunity/DTH is a double-edged sword that may contribute to both clearance of the etiologic agent and tissue damage.

Rheumatoid arthritis (RA) is an autoimmune disease characterized by the elicitation and activation of a number of leukocyte populations within both the synovial space and joint tissue. The recruited leukocytes subsequently play an instrumental role in synovial cell proliferation, pannus formation, and bone erosion. Although it is know that leukocytes are important participants in the evolving joint pathology, the mechanism responsible for the successful elicitation of cells to the joint is not clear. A number of studies have identified an association of specific cytokines, including chemokines, with active arthritis, but longitudinal analyses of cytokine expression and the causal role of these mediators have not been defined. Animal models and cell culture systems have proved useful in identifying the expression of various cytokines during the maintenance of chronic joint inflammation. In addition, animal models have provided important information regarding the kinetic production and contribution of specific mediators to the development of experimental arthritis. These studies provide insights into the potential mechanisms for leukocyte involvement in inflammatory joint disease.

TLR3 is expressed inside airway epithelial cells and transduces synthetic dsRNA signals. These signals may increase expression of inflammatory cytokines, chemokines and ICAM-1 through activation of transcription factors NF-kappaB and/or IRF3 in airway epithelial cells.

We have examined the expression and function of the angiogenic factor, vascular endothelial growth factor (VEGF) during the evolution of type II collagen-induced arthritis (CIA). Biologically active VEGF was expressed along a time course that paralleled the expression of two specific VEGF receptors, Flk-1 and Flt-1, and the progression of joint disease. Moreover, levels of VEGF expression correlated with the degree of neovascularization, as defined by vWF levels, and arthritis severity. Macrophage- and fibroblast-like cells, which infiltrated inflamed sites and were then activated by other inflammatory mediators, are probably important sources of VEGF and may thus regulate angiogenesis during the development of CIA. Administration of anti-VEGF antiserum to CIA mice before the onset of arthritis delayed the onset, reduced the severity, and diminished the vWF content of arthritic joints. By contrast, administration of anti-VEGF antiserum after the onset of the disease had no effect on the progression or ultimate severity of the arthritis. These data suggest that VEGF plays a crucial role during an early stage of arthritis development, affecting both neovascularization and the progression of experimentally induced synovitis.

Swmmar~Neutrophil (polymorphonuclear leukocyte [PMN]) sequestration is one of the histologic hallmarks of an acute inflammatory response. During the natural evolution of an inflammatory response, PMNs are often replaced by mononuclear cells. This shift in the elicitation of specific leukocyte populations usually occurs as the inflammatory lesion enters either the repair/resolution stage or progresses to a chronic inflammation. To elucidate a potential mechanism for the temporal change from predominantly PMN recruitment to the presence of monocytes, we postulated that PMNs could be a rich source of monocyte chemotactic factors. In our studies, we have identified a dose-dependent induction of monocyte chemotactic activity by PMNs treated with lipopolysaccharide (LPS; 1-100 ng/ml). Interestingly, this monocyte chemotactic activity was significantly attenuated in the presence of neutralizing anti-human macrophage inflammatory protein lc~ (MIP-I~x) antibodies. Moreover, immunolocalization studies demonstrated the expression of MIP-lot by stimulated PMNs. These findings showed that a significant amount of PMN-derived monocyte chemotactic activity was attributable to MIP-loe. Subsequent characterization of MIP-lo~ steadystate mRNA and antigen expression demonstrated both a dose-and time-dependent production by LPS-treated PMNs. Granulocyte/macrophage colony-stimulating factor (GM-CSF), a potent PMN activator, failed to induce the expression of MIP-lc~ over a wide range of concentrations. However, PMNs stimulated in the presence of both LPS and GM-CSF resulted in a synergistic expression pattern for MIP-lc~. PMNs stimulated in the presence of both GM-CSF and LPS demonstrated an enhanced and prolonged expression for both MIP-loe mRNA and antigen, as compared with LPS alone. Messenger RNA stabilization analyses demonstrated that MIP-lc~ mRNA isolated from PMNs stimulated in the presence of GM-CSF and LPS had a prolonged mRNA tl/2, as compared with LPS alone. These findings support the notion that PMNs are capable of producing MIP-lol in the presence of LPS, and that GM-CSF can influence this production through prolongation of MIP-lc~ mRNA tl/2. The production of PMN-derived MIP-lcx, in association with the expression of appropriate adhesion molecules at a site of inflammation, may be one of the central events that contributes to the temporal shift from predominantly PMNs to monocytes during the evolution of inflammation.

No abstract