Cord factor

Cord factor is composed of trehalose dimycolate, a glycolipid located in the outer mycolic acid layer of the mycobacterial cell wall. Its name derives from the characteristic serpentine cord-like arrangement that virulent strains of M. tuberculosis exhibit when grown in culture, a pattern not seen in avirulent strains. Functionally, cord factor is a major virulence factor: it activates macrophages to release TNF-alpha, contributing to granuloma formation and caseous necrosis, and it inhibits neutrophil chemotaxis, impairing the innate immune response. It also disrupts mitochondrial function in host cells and has adjuvant properties, historically used in experimental vaccine research. Cord factor contributes to the destruction of host tissue and the chronic, smoldering inflammatory response characteristic of tuberculosis. Its presence correlates with virulence—strains lacking cord factor tend to be less pathogenic. Clinically, understanding cord factor helps explain the pathogenesis of caseating granulomas seen in TB, a hallmark finding on pathology (central caseous necrosis surrounded by epithelioid histiocytes, Langhans giant cells, and lymphocytes). This is tested in the context of M. tuberculosis virulence factors alongside sulfatides (which inhibit phagolysosome fusion) and mycolic acids (contributing to acid-fastness).