DPP4 and central nervous system disorder: Of interest, HLA-DR, a marker of cellular activation, was higher on CD8 T cellsand CD4 T cells in the autism group compared with typically developing controls.The T cell marker CD26/dipeptidyl peptidase IV, which is associated with aneffector cell phenotype and is markedly elevated in human CNS disorders such asmultiple sclerosis, was increased on CD8 T cells in autism compared withcontrols.