DPP4 and infection: The functions already proposed for sCD26, inducing human neutrophil chemorepulsion [22,23,24] or proliferation of human smooth muscle cells [28] have shown clinical consequences in inflammatory diseases including infection, autoimmune [22,23,24], and probably cancer [25,26,27], so clarifying the relationship between the CD26 expression on lymphocytes and sCD26/DPP4 may help to advance in the knowledge of their physiological roles and therapeutic approaches [18,19,20,34,35,57,58,59,60,61,62].