Fig. 3: GM-CSF drives BM myelopoiesis and organ inflammation in SpA.

a Representative intracellular cytokine staining from CD4 T cells from popliteal lymph nodes and paw joints of mice culled 5 weeks after SpA induction. Frequencies and absolute numbers of articular GM-CSF⁺ CD4 T cells in healthy versus spondyloarthritic SKG mice; cells were incubated with brefeldin A, PMA and ionomycin before staining. b Absolute numbers of GM-CSF⁺ CD4 T cells in SI LPL and total GM-CSF protein in SI quantified by ELISA, n = 5 per group. c–h Curdlan-triggered SKG mice were treated for the entire duration of the experiment (6–7 weeks) with anti-GM-CSF or isotype control antibodies and compared to healthy (steady state) SKG controls. c LSK staining and frequencies of LT-HSCs and MPPs populations in BM. d GMP and MEP staining, GMP:MEP ratio, and frequencies of GMP and CLP populations in BM. e Frequencies of neutrophils, erythroid cells and B cells in BM. f Staining and absolute numbers of neutrophils in joints (left) and SI (right). g Mean arthritis scores (n = 7 mice in each group), histological arthritis scores and increase in ankle size (left). Representative µCT scans of isotype or anti-GM-CSF antibody treated SpA mice and changes in bone surface to volume ratio pooled from two independent experiments (right). Scale bars = 1 cm. h Representative photomicrographs of small intestinal sections (magnification ×4 and ×10) and histological enteritis scores. Scale bars = 1 cm (left panels) and 200 µm (right panels). i Clinical arthritis score of mice that received isotype or anti-GM-CSF antibody injections starting 9 days after injection of curdlan, when the first clinical signs of arthritis appeared (n = 7 mice in each group). Groups were compared using the Wilcoxon matched-pairs signed rank test. Data are representative of two independent experiments (a–h). Dots represent individual mice; horizontal bars indicate mean. Groups were compared using Mann–Whitney U tests unless noted otherwise. Source data are provided as Source Data file.