ICOS and autoimmune disease: Increased frequencies of TFH-like cells are often observed in patients with autoimmune diseases including SLE6, and studies of Roquinsan mice show that overexpression of IFNγ and ICOS, a co-stimulatory molecule highly expressed in TFH cells37, 38, promotes TFH cell development, which in turn spontaneously induces a lupus-like autoimmune syndrome39, 40.