CD40LG and viral infectious disease: Several studies demonstrated that the presence of appropriate inflammatory and co-stimulatory maturation signals, such as pathogen-associated molecular patterns (PAMPs), TLR ligands, type I IFNs, CD80/CD86, and CD70 (119, 120) as well as CD40 ligand (CD154) provided by CD4+ T cells (“DC licensing”) is essential for DCs to properly activate CTLs in viral infections (118).