Fig. 7: IL-33 can promote GM-CSF production by mast cells during SpA.

a IL-33 protein levels from joints and SI of healthy and spondyloarthritic mice, n = 13 mice per group. b BMMC were stimulated with PBS or IL-33 for 16 h and secreted IL-6 and GM-CSF quantified by ELISA. Error bars = SEM of 3 independent experiments. c–i SpA-triggered male SKG mice were injected IP twice weekly with PBS or 1 µg of rIL-33. c Experimental protocol. d GM-CSF protein levels from joints and SI from PBS or IL-33 treated mice, n = 7 mice per group. e Frequencies and absolute numbers of splenic MC. f Staining of intracellular cytokines (compared to GM-CSF FMO control) and frequencies of GM-CSF⁺ cells among splenic MCs. g Frequencies of LT-HSCs and MPPs in BM (left). Staining of GMPs and MEPs in BM (middle). Frequencies of GMPs and neutrophils in BM (right). h Absolute numbers of GMP and neutrophils in spleens (left) and joints (right). Dots represent individual mice; horizontal bars indicate mean. i Mean arthritis scores (n = 7 mice in each group) and increase in ankle thickness. j–k SKG females were injected with ST2-Fc or control Fc fragment for 5 weeks after injection of curdlan. j Frequency of GM-CSF⁺ mast cells in SI of Fc control- and ST2-Fc-treated mice after 5 weeks. k Change in paw size (left) and clinical arthritis score (right) in Fc control- and ST2-Fc-treated mice after 2 (top) or 5 (bottom) weeks. l SKG males were injected with curdlan then IL-33, with or without isotype or anti-GM-CSF antibodies. Dots represent individual mice; horizontal bars indicate mean. Clinical arthritis score (left) and change in ankle thickness (right) after 4 weeks. Data are representative of three independent experiments (a−i) or pooled from two independent experiments (k). Groups were compared using Mann–Whitney U tests. Source data are provided as Source Data file.