MAPK8 and neoplasm: From functional aspects, precursors of IL-38 can upregulate the expression levels of IL-6 by human macrophages in apoptotic tumor cell conditioned medium (ACM), whereas the truncated forms of IL-38 downregulate expression levels of IL-6 secretion through the attenuation of JNK/AP-1 signaling as a downstream process to IL-1RAPL1.