Eukaryotic cilia are assembled via intraflagellar transport (IFT) in which large protein particles motor along ciliary microtubules. IFT20 functions in the delivery of ciliary membrane proteins from the Golgi complex to the cilium. IFT20 is the smallest member of the intraflagellar transport protein (IFT) complex B. It is involved in cilia formation. IFT20 in the early stage of T-cell development inhibited collagen-induced arthritis (CIA) development through regulating T-cell development and the expression of critical cytokines. The intraflagellar transport protein 20 (IFT20), a component of the intraflagellar transport system, controls polarized traffic during immune synapse assembly. IFT20 is therefore required for the delivery of the intracellular pool of LAT to the immune synapse in naive primary T lymphocytes and for effective T-cell responses in vivo. IFT20 is essential for male fertility and spermiogenesis in mice, and its major function is to transport cargo proteins for sperm flagella formation.