Repeated TLR9 stimulation results in macrophage activation syndrome–like disease in mice

Abstract

Hemophagocytic lymphohistiocytosis (HLH) and macrophage activation syndrome (MAS) are 2 similar diseases characterized by a cytokine storm, overwhelming inflammation, multiorgan dysfunction, and death. Animal models of HLH suggest that disease is driven by IFN-γ produced by CD8 + lymphocytes stimulated by persistent antigen exposure. In these models and patients with "primary" HLH, the antigen persists due to genetic defects, resulting in ineffective cytotoxic responses by CD8 + T cells and poor pathogen clearance. However, infectious triggers are often not identified in patients with MAS, and some patients with HLH or MAS lack defects in cytotoxic T cell killing. Herein, we show that repeated stimulation of TLR9 produced an HLH/ MAS-like syndrome on a normal genetic background, without exogenous antigen. Like previous HLH models, TLR9-induced MAS was IFN-γ dependent; however, unlike other models, disease did not require lymphocytes. We further showed that IL-10 played a protective role in this model and that blocking IL-10 signaling led to the development of hemophagocytosis. IL-10 may therefore be an important target for the development of effective therapeutics for MAS. Our data provide insight into MAS-like syndromes in patients with inflammatory diseases in which there is chronic innate immune activation but no genetic defects in cytotoxic cell function.

Macrophage activation syndrome as part of systemic juvenile idiopathic arthritis: diagnosis, genetics, pathophysiology and treatment

“…Recently, a new murine model of MAS induced by repeated stimulation of Toll-like receptor (TLR) 9 may provide some insight. 52 The rationale for this model involves multiple observations. Gene signatures consistent with chronic TLR/IL-1b signaling are present in sJIA patients.…”

“…68 Whether the IFNg responding macrophage becomes a hemophagocyte, or whether it induces another cell type to become a hemophagocyte is unclear. Furthermore, although the presence of hemophagocytosis is correlated with development of anemia 68 and worsened disease activity, 52 there is of yet no direct demonstration that hemophagocytes are directly pathogenic. In fact, some authors have found potentially anti-inflammatory/regulatory properties for hemophagocytes.…”

Does Viral Hemorrhagic Fever Represent Reactive Hemophagocytic Syndrome?

“…This accumulation of antigen results in overstimulation of the frustrated lymphocytes, copious release of cytokines (a cytokine storm), and the resulting multiorgan pathology 13 . Such situations may arise when cytotoxic granule function is genetically intact as well 16 . Additionally, patients with systemic lupus erythematosus, systemic juvenile idiopathic arthritis, and 13 .…”

“…For instance, in mice, excessive Toll-like receptor 9 stimulation can lead to a perforin-independent -and indeed lymphocyte-independent -cytokine-driven HPS 16 . Given the clinical overlap between many features of VHF and rHPS, it is intriguing to speculate whether similar pathophysiology is at play at least in part in VHF.…”

“…Nevertheless, it is possible that the increased serum levels of IL-1RA and IL-10 reflect the immune system's attempt to dampen the overexuberant immune response in the sickest Ebola-infected patients experiencing MODS. Indeed, blockade of IL-10 was required to demonstrate hemophagocytosis in a murine model of rHPS 16 . Moreover, the concept of immune suppression of Ebola VHF has been recently considered by others 26 .…”