Background: Lung disease is a potentially fatal complication of Stills Disease (including systemic juvenile idiopathic arthritis and adult-onset SD), strongly linked to occurrence of macrophage activation syndrome (MAS), an IFN-gamma-driven cytokine storm. SD-associated lung disease in patients treated with anti-cytokine biologic drugs have distinct clinical features and develop pulmonary alveolar proteinosis (PAP), indicative of lung macrophage dysfunction. However, the etiology of SD-associated lung disease remains unclear. We have previously demonstrated that the TLR9-induced mouse model of MAS demonstrates IFN-gamma-driven lung inflammation replicating several key features of SD-associated lung disease. The relative contributions of IL-1 and IFN-gamma signaling in driving pulmonary inflammation is unknown.

Objectives: To define activated lung myeloid populations in the TLR9-induced mouse model of MAS, and impact of IL-1 and IFN-gamma blockade.

Methods: Wild type (WT) or IL-1R-/- C57BL/6J mice were sequentially intraperitoneal (IP) injected 5 times with ODN1826 (CpG) over 10 days. For IFN-gamma blockade, mice were given IP injections of isotype control or XMG1.2 (anti-IFNg) in conjunction with CpG. Lung tissue was harvested, digested, and stained against CD45, CD11b, CD11c, CD24, CD64, MHC class II, SiglecF, Ly6C, and Ly6G, prior to analysis using the Cytek Aurora full spectrum cytometry system.

Results: In TLR9-induced MAS, we observed marked changes in the lung myeloid compartment. Along with a small but significant 2-fold increase in CD11bLo/SiglecF+ alveolar macrophages, there was a 10-fold increase in CD103+ pulmonary DCs, 30-fold increase in CD11b+/SiglecF- interstitial macrophages, and 5-10-fold increase in less mature Ly6C- and Ly6C+/SiglecF- monocytes and macrophages, compared to PBS-treated control animals. Our previous work has shown that when mice were treated with anti-IFN-gamma, there was a significant reduction in both systemic features and alveolar macrophage activation. Here, we also saw significantly reduced accumulation of interstitial macrophages as well as pulmonary DC, but no change in recruitment of Ly6C- and Ly6C+/SiglecF- monocytes and macrophages, compared to isotype-control-treated animals. When MAS was induced in IL-1R-/- mice, most systemic features of MAS were similar, although there was a small but significant reduction in splenomegaly and anemia compared to WT animals. However, in contrast to IFN-gamma blockade, recruitment of most myeloid cell populations to the lungs was unchanged in IL-1R-/- mice. Specifically there was no significant difference in accumulation of interstitial macrophages, pulmonary DC, or Ly6C- and Ly6C+/SiglecF- monocytes and macrophages. Notably however, IL-1R-/- mice showed significant fewer SiglecF+ alveolar macrophages than WT mice, with no increase observed compared to PBS-treated animals.

Conclusions: In the TLR9-induced model of MAS, we find that IFN-gamma blockade prevents accumulation of interstitial macrophages and pulmonary DC. In contrast, IL-1 blockade only impacts alveolar macrophage abundance while failing to prevent recruitment of other myeloid populations. Given that anti-IL-1 therapy does not prevent SD-associated LD, these findings have important implications for lung inflammation development under anti-cytokine therapy.

REFERENCES: NIL.

Acknowledgments: NIL.

Disclosure of Interests: Richard Chhaing: None declared, Natsumi Inoue: None declared, Grant Schulert SOBI.