CD40 and thromboangiitis obliterans: In other words, PD-L1 inhibits the activity of T cells, and thus weakens T cell-induced TAO-OF activation via the CD40-CD40L costimulatory pathway, thereby down-regulating the phosphorylation levels of p38, ERK1/2, JNK, and NF-κB p65 pathway proteins, and significantly reducing the production of sICAM-1, IL-6, IL-8, and HA in TAO-OFs (Figure 7).