Interleukin 38 (IL-38) is a 16.87 kDa cytokine with 152 amino acid residues and a member of the interleukin-1 (IL-1) family. IL-38 is primarily secreted from basal epithelia of the skin and B cells of the tonsil, spleen, and thymus. It plays essential roles in inflammation and host defense by mediating NF-kappaB, AP1, and JNK signaling pathways when IL-38 binds to the receptors like IL1RAPL1 and IL-36R. In addition, IL-38 participates in down-regulating cell proliferation, migration, and up-regulating IL-6 and IL-10.