C3 and Arthritis: Lung involvement prior the onset of arthritis; increase in ankle thickness with high levels of anti‐CII antibodies; inflammatory cell infiltration(T cells and CD11bhi macrophages), ACPAs, C3 deposited in the subpleural region of the lung, increased cytokines of IL‐1β, IL‐6, IFN‐γ, TNF‐α levels, IL‐4, IL‐17, CCL3, and CCL4