TLR4 and endometriosis: In particular, Gram-negative bacteria such as Proteobacteria, which were found to be higher in endometriosis, contain in their cell wall an enterotoxin called lipopolysaccharide (LPS) that promotes inflammation through binding to toll-like receptor-4 (TLR-4), contributing to the onset and progression of endometriosis lesions [164,166,167].