Muramyl dipeptide (MDP) and lipopolysaccharide (LPS) from Escherichia coli were tested for the ability to influence superoxide anion (O2-) release from guinea pig phagocytes. Both MDP and LPS alone did not, by themselves, stimulate O2 release by macrophages and polymorphonuclear leukocytes. However, the preincubation of macrophages with MDP or LPS primed the macrophages to release an enhanced amount of O2 when stimulated by cytochalasin E and wheat germ agglutinin. When polymorphonuclear leukocytes were treated in the same way, only LPS showed an enhancing effect. MDP enhanced NADPH oxidase activity of macrophages, which is probably the reason for enhanced O2 release by MDP.Peptidoglycans are structures common to bacterial cell walls. Muramyl dipeptide (MDP), Nacetylmuramyl-L-alanyl-D-isoglutamine, is a minimal structure in peptidoglycans responsible for many activities of bacteria, including immunoadjuvant effect (7). Although the injection of a Freund-type water-in-oil emulsion alone generally induces only macrophage accumulation or sometimes foreign body granulomas in the draining lymph nodes, the incorporation of MDP in the emulsion causes remarkable qualitative and quantitative changes, such as the development of extensive epithelioid granulomas indistinguishable from those evoked by tubercle bacilli and a marked infiltration of polymorphonuclear leukocytes (PMN) (8, 28).MDP activates macrophages to become bactericidal (11), and epithelioid cells appear to be bactericidal against tubercle bacilli (3). However, the mechanism causing macrophages to become bactericidal through MDP is not yet known. It is also not known why PMN accumulate in the MDP-induced granulomas and whether PMN are affected by MDP. To understand these unsolved questions, we investigated, in the present study, the effect of MDP on superoxide anion (O2-) release from macrophages or PMN, because O2 has been known to contribute to microbicidal activity of phagocytes (5,6,17) and to cause the generation of chemotactic factor(s) for PMN (15,25,31). Guinea pigs were used because this animal species has been mostly used for the study of granuloma formation by MDP. Since bacterial lipopolysaccharide (LPS) shares many biological activities with MDP, LPS was also studied in parallel with MDP.
MATERIALS AND METHODSReagents. Cytochalasin E (CyE), superoxide dismutase (type I, from bovine blood), ferricytochrome c (type VI, from horse heart), and NADPH were purchased from Sigma Chemical Co., St. Louis, Mo. Wheat germ agglutinin (WGA) was purchased from P-L Biochemicals, Inc., Milwaukee, Wis. Renex 30, polyoxyethylene tridecyl ether, a product of ICI Americas, Inc., Wilmington, Del., was the generous gift of M. Nakamura, Kyushu University; Hanks balanced salt solution (HBSS) was purchased from Nissui Pharmaceutical Co., Ltd., Tokyo, Japan. Medium 199 and fetal bovine serum were purchased from GIBCO Laboratories, Grand Island, N.Y. Lipopolysaccharide (LPS) from Escherichia coli (serotype 0.127:B8, type I) was purchased from Sigma Chemical Co. MDP and its ...
