Hyaluronan fragments synergize with interferon-gamma to induce the C-X-C chemokines mig and interferon-inducible protein-10 in mouse macrophages.

Hallmarks of chronic inflammation and tissue fibrosis are increased influx of activated inflammatory cells, mediator release, and increased turnover and production of the extracellular matrix (ECM). Recent evidence has suggested that fragments of the ECM component hyaluronan play a role in chronic inflammation by inducing macrophage expression of chemokines. Interferon-gamma (IFN-gamma), an important regulator of macrophage functions, has been shown to induce the C-X-C chemokines Mig and IP-10. These chemokines affect T-cell recruitment and inhibit angiogenesis. The purpose of this investigation was to determine the effect of hyaluronan (HA) on IFN-gamma-induced Mig and IP-10 expression in mouse macrophages. We found a marked synergy between HA and IFN-gamma on Mig and IP-10 mRNA and protein expression in mouse macrophages. This was most significant with Mig, which was not induced by HA alone. The synergy was specific for HA, was not dependent on new protein synthesis, was not mediated by tumor necrosis factor-alpha, was selective for Mig and IP-10, and occurred at the level of gene transcription. These data suggest that the ECM component HA may influence chronic inflammatory states by working in concert with IFN-gamma to alter macrophage chemokine expression.

Inhibition of interferon gamma induced interleukin 12 production: a potential mechanism for the anti-inflammatory activities of tumor necrosis factor.

Inflammation is associated with production of cytokines and chemokines that recruit and activate inflammatory cells. Interleukin (IL) 12 produced by macrophages in response to various stimuli is a potent inducer of interferon (IFN) gamma production. IFN-gamma, in turn, markedly enhances IL-12 production. Although the immune response is typically self-limiting, the mechanisms involved are unclear. We demonstrate that IFN-gamma inhibits production of chemokines (macrophage inflammatory proteins MIP-1alpha and MIP-1beta). Furthermore, pre-exposure to tumor necrosis factor (TNF) inhibited IFN-gamma priming for production of high levels of IL-12 by macrophages in vitro. Inhibition of IL-12 by TNF can be mediated by both IL-10-dependent and IL-10-independent mechanisms. To determine whether TNF inhibition of IFN-gamma-induced IL-12 production contributed to the resolution of an inflammatory response in vivo, the response of TNF+/+ and TNF-/- mice injected with Corynebacterium parvum were compared. TNF-/- mice developed a delayed, but vigorous, inflammatory response leading to death, whereas TNF+/+ mice exhibited a prompt response that resolved. Serum IL-12 levels were elevated 3-fold in C. parvum-treated TNF-/- mice compared with TNF+/+ mice. Treatment with a neutralizing anti-IL-12 antibody led to resolution of the response to C. parvum in TNF-/- mice. We conclude that the role of TNF in limiting the extent and duration of inflammatory responses in vivo involves its capacity to regulate macrophage IL-12 production. IFN-gamma inhibition of chemokine production and inhibition of IFN-gamma-induced IL-12 production by TNF provide potential mechanisms by which these cytokines can exert anti-inflammatory/repair function(s).

Induction of IL-12 and chemokines by hyaluronan requires adhesion-dependent priming of resident but not elicited macrophages.

Components of the extracellular matrix (ECM) can regulate leukocyte activation and function at inflammatory sites. Low molecular weight fragments of the ECM glycosaminoglycan hyaluronan (LMW-HA) that accumulate in inflammation, but not the ubiquitous high molecular weight form of HA (HMW-HA), have been shown to induce cytokine and/or chemokine production by alveolar and bone-marrow derived macrophages. To determine the cellular requirements for responsiveness to HA, we compared the effects of HMW-HA and LMW-HA on resident and thioglycollate-elicited murine peritoneal macrophages. We demonstrate that treatment of elicited macrophages with LMW-HA, but not with HMW-HA, stimulated production of the chemokines RANTES and macrophage inflammatory protein-1alpha and -1beta. Further, we demonstrate that LMW-HA induced the production of biologically active IL-12, a proinflammatory cytokine not previously known to be regulated by cell-matrix interactions. The LMW-HA-induced production of IL-12 by elicited macrophages was inhibited by an anti-CD44 mAb that blocks HA binding. In contrast to elicited macrophages, freshly explanted resident peritoneal macrophages did not respond to LMW-HA. However, preculture in vitro before stimulation led to adhesion-dependent priming for LMW-HA-induced cytokine and chemokine production by resident macrophages. These results provide further evidence of the potential importance of CD44/LMW-HA interactions in regulating the immune response at sites of inflammation and demonstrate that the state of differentiation of macrophages may determine their sensitivities to matrix components.