A serum lectin (mannan-binding protein) has complement-dependent bactericidal activity.
Serum mannan-binding protein (MBP), which is a lectin specific for mannose and N-acetylglucosamine and is known to activate complement via the classical pathway, has been revealed to have a complement-dependent bactericidal activity, as tested on rough strains of Escherichia coli, K-12 and B. The bacteria, which had been sensitized with purified human serum MBP in the presence of Ca2+, followed by incubation with guinea pig complement, showed a marked decrease of colony forming ability compared with those not sensitized with the lectin. The bactericidal effect depended on the concentrations of the lectin and complement. The C4-dependency of the reaction indicated that the complement-dependent bactericidal action by MBP is expressed through the classical pathway. The bacteria were aggregated by the lectin. Scatchard plot analysis of 125I-labeled MBP binding to the bacteria showed that the dissociation constant (Kd) and the maximum binding capacity were 6 x 10(-9) M and 30,000 molecules of MBP per cell, respectively. The binding was inhibited by mannose, N-acetylglucosamine, N-acetylmannosamine, L-fucose, manno-heptulose, and sedoheptulose, suggesting that MBP recognized L-glycero-D-manno-heptose and N-acetylglucosamine constituting the core oligosaccharide of the E. coli K-12 cell wall, and L-glycero-D-manno-heptose for E. coli B. These findings suggest the physiological significance of the serum lectin in host defense, being consistent with the avirulence of E. coli rough strains in mammals.
Kawasaki
N
N
College of Medical Technology, Faculty of Pharmaceutical Sciences, Kyoto University.
Kawasaki
T
T
Yamashina
I
I
D000818:Animals; D001770:Blood Bactericidal Activity; D002352:Carrier Proteins / Q000097:blood* / Q000378:metabolism / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D002473:Cell Wall / Q000378:metabolism; D037222:Collectins; D003181:Complement C4 / Q000494:pharmacology; D004926:Escherichia coli / Q000378:metabolism; D006168:Guinea Pigs; D006801:Humans; D007457:Iodine Radioisotopes; D011135:Polysaccharides, Bacterial / Q000378:metabolism; D011817:Rabbits
D002352:Carrier Proteins; D037222:Collectins; D003181:Complement C4; D007457:Iodine Radioisotopes; D011135:Polysaccharides, Bacterial