TLR4 and epididymitis: Considering the frequency of E. coli-induced epididymitis in men (see Region-Specific Responses in Human Epididymitis), lipopolysaccharide (LPS), a structural component of the outer membrane of Gram-negative bacteria such as E. coli, can be explored as agonist of the toll-like receptor 4 (TLR4) to investigate the role of TLR4 signaling in epididymitis pathogenesis.