TNF and endometriosis: As IL-33 is considered an alarmin, we found that when NESCs and HESCs were stimulated with inflammatory cytokines IL-1β or TNF-α, which are known to be upregulated in patients with endometriosis [56], the gene expression levels of IL-33 were significantly elevated as compared with unstimulated controls (all p-values ≤ 0.038; Figure 2A).