NRP1 and Autoimmunity: During antigen recognition, Nrp-1 expression facilitates Treg interaction with DCs to suppress T-cell activation.38 On the other hand, semaphorin-4a ligation of Nrp-1 on Treg cells can maintain Treg stability and function through induction of PTEN.39 Although deficiency of Nrp-1 does not affect the ability to suppress autoimmunity and maintain immune homeostasis, deficiency of Nrp-1 on Treg cells leads to enhanced immune response in tumor model.39, 40 These suggest that Nrp-1 regulation of Treg cells needs further investigations.