PIP binds to CD4 and inhibits the CD4-HLA-DR interaction,34 induces differentiation of naive T cells into CD4(+) CD25(+) forkhead box P3(+) (FOXP3(+)) Treg cells,35 and exerts both local and systemic immunosuppressive effects in mouse contact dermatitis.26 This evidence concerns the gene CD4 and contact dermatitis.