Poster Presentation Lorne Infection and Immunity 2013

Interleukin (IL)-37 exerts its anti-inflammatory functions by complexing with SIGIRR and IL-18Rα (#153)

Ina Rudloff 1 , Camden Lo 2 , Jarod A Zepp 3 , Tania Azam 3 , Suzhao Li 3 , Cecilia Garlanda 4 , Alberto Mantovani 4 , Philip Bufler 5 , Charles A Dinarello 3 , Claudia A Nold-Petry 1 3 , Marcel F Nold 1 3
  1. The Ritchie Centre, Monash Institute of Medical Research, Melbourne, VIC, Australia
  2. Monash Micro Imaging, Monash University, Melbourne, VIC, Australia
  3. Department of Medicine, University of Colorado, Denver, USA
  4. Istituto Clinico Humanitas, Milan, Italy
  5. Children’s Hospital, Ludwig-Maximilians University, Munich, Germany

IL-37 is an extraordinarily potent anti-inflammatory IL-1 family member effective against a broad spectrum of inflammatory assaults in cell lines, PBMC and mice transgenic for IL-37 (IL-37tg). One mechanism of this beneficial effect is via intracellular association with Smad3; however, a cell-surface receptor for IL-37 is unknown.
Here, we show that to block inflammation, IL-37 requires IL-18 receptor alpha (IL-18Rα) and SIGIRR, a so-far orphaned member of the IL-1R family.
In PBMC, which naturally express IL-37, knockdown of SIGIRR resulted in a 3-fold increase in IL-1β and IL-6. Though IL-1β- and LPS-induced pro-inflammatory cytokines were markedly reduced in THP-1 cells transfected with IL-37, simultaneous transfection of IL-37 and siRNA to SIGIRR significantly attenuated IL-37-mediated cytokine reduction (83% inhibition with IL-37 in the presence of SIGIRR, 34% with SIGIRR silenced). The anti-inflammatory function of IL-37 was also attenuated when IL-18Rα was silenced or blocked in A549 cells, PBMC and MEF. To eliminate SIGIRR´s contribution to IL-37´s functions in vivo, we created SIGIRR-/- mice expressing IL-37. When these IL-37tg-SIGIRR-/- mice and IL-37tg animals were injected with LPS, the protective effect observed in IL-37tg was markedly reduced in the IL-37tg-SIGIRR-/- strain.
By immunofluorescence, we observed that IL-37 associates with SIGIRR and IL-18Rα in LPS-stimulated RAW macrophages and IL-1β-treated A549 cells, both transfected with IL-37. Using proximity ligation assays in PBMC, we demonstrated sub-40nm co-localization of the three pairs IL-37-SIGIRR, IL-37-IL-18Rα and SIGIRR-IL-18Rα. FRET analysis in PBMC revealed that IL-37-SIGIRR interaction peaks 30min after LPS stimulation, decreasing to non-stimulated levels by ~4h.
We conclude that IL-37 limits inflammation by associating with SIGIRR and IL-18Rα, suggesting that SIGIRR-IL-18Rα functions as the cell-surface receptor for IL-37.