CSF2 and Arthritis: Following the initiation of arthritis, arthritogenic Th17 cells together with FLSs and synovial ILCs orchestrate an inflammatory cascade to amplify chronic joint inflammation by GM-CSF from various sources subjected to different immunological stimuli, resulting in the activation of synovial macrophages and their abundant production of pro-inflammatory cytokines such as IL-1, IL-6, and TNFα (Figure 1).