FOS and rheumatoid arthritis: Activator protein 1 (AP‐1) is generally a heterodimer composed of proteins of the Jun, Fos and activating transcription factor protein (ATF) families.15, 16 As a transcription factor, AP‐1 switches on targeted gene expression and upregulates cytokine expression, contributing to tissue inflammation in diseases such as rheumatoid arthritis, psoriasis, and psoriatic arthritis.17, 18 In acute brain injury such as ICH, however, little is known about the role of AP‐1 in neuroinflammation formation.