Granuloma formation by synthetic bacterial cell wall fragment: muramyl dipeptide

A synthetic muramyl dipeptide, N-acetylmuramyl-L-alanyl-D-isoglutamine, which possesses the same structure as that of a part of the peptidoglycan monomer of wax D of tubercle bacilli or bacterial cell walls was found to induce, when injected in water-in-oil emulsion, massive granulomas often accompanying abscesses in the site of injection and draining lymph nodes of guinea pigs and rats. The granulomas were composed mainly of epithelioid cells 2 weeks after injection and were indistinguishable from those induced by tubercle bacilli. The granulomas induced in rats were less mature than those induced in guinea pigs. Allergic reaction appeared to play no important role in the development of the muarmyl dipeptide-induced granuloma.