SLPI and parasitic infectious disease: After some parasite infections, Treg cells activate specific genes, such as those encoding CD103, Foxp3, glucocorticoid-induced TNFR family related gene (GITR), OX40 (CD134), CTLA-4, secretory leukocyte peptidase inhibitor (Slpi), granzyme B (Gzmb), fatty acid-binding protein 5 (Fabp5), nuclear factor, interleukin 3 regulated (Nfil3), suppressor of cytokine signaling 2 (Socs2), G protein-coupled receptor 177 (Gpr177), and killer cell lectin-like receptor subfamily G, member 1 (Klrg1) [10]–[14].