PTGS2 and neoplasm: Recruited constitutive cyclooxygenase-2 (COX-2)-expressing MSCs produced prostaglandin E2 (PGE2), which protected epithelial stem cells against radiation-induced apoptosis in mice.42,43 In the context of TLR4, dendritic cells utilized TLR4/MyD88 to process antigens from dying tumor cells, enhancing antitumor immunity during radiotherapy.