GM-CSF production by immune cells in steady state and autoimmune neuroinflammation mapped using fate reporting mice

The full GM-CSF expression spectrum in immune cells remains unclear, while CD4□ T cells are the primary source. Using novel GM-CSF reporter/fate reporter transgenic mice, we tracked ongoing and past (YFP ⁺ ) GM-CSF expression in various immune cells. GM-CSF was produced by diverse immune cells, including CD4 ⁺ , CD8 ⁺ , γδ T, NK, B, and CD11b ⁺ cells, with expression patterns varying by cell type and organ with liver CD4 ⁺ T cells and NK cells showing the highest expression history in both naïve and mice with EAE. GM-CSF expression was transient and permanently lost in most cells over time. In a mouse model of multiple sclerosis, effector memory CD4□ T cells were the dominant CNS GM-CSF source, with higher expression than in other organs. CD4 ⁺ YFP ⁺ T cells, strongly expressing CXCR6, produced multiple cytokines. Transcriptomic analysis showed distinct gene expression profiles in effector memory CD4 ⁺ T cells compared to naïve cells. YFP□ Tregs represent functionally distinct subsets mirroring effector Th cells, expressing cytokines associated with Th lineages, especially during neuroinflammation. These findings identified distinct GM-CSF cellular sources across organs, highlighting a transient tissue microenvironment influence on GM-CSF production linked to CXCR6 expression.