Inducible T‐cell co‐stimulator: Signaling mechanisms in T follicular helper cells and beyond

Human patients with homozygous null mutations in the ICOS gene suffer from recurrent infections due to humoral immune defects. Studies on human patients and mouse models have shown that inducible T-cell co-stimulator (ICOS)-deficient individuals cannot form T follicular helper (Tfh) cells, a group of CD4 T cells that migrate into B cell follicles and facilitate germinal center (GC) reactions. ICOS-induced phosphoinositide 3-kinase signaling...