title: MC22-33F monoclonal antibody shows unmasked polar head groups of choline-containing phospholipids in cartilage and bone.
abstract: The importance of the role lipids may have in biological calcification, and the paucity and poor specificity of the methods available for studying their ultrastructural localization, call for further investigations involving new techniques. The monoclonal antibody MC22-33F displays a specific reaction with phosphatidylcholine, sphingomyelin and dimethylphosphatidylethanolamine, as confirmed by its reaction with synthetic lyposomes of pure phosphatidylcholine. For this reason, it was used to demonstrate the presence and ultrastructural localization of choline-containing phospholipids in calcifying cartilage and bone. The MC22-33F MAb immunoreaction was found in the cytoplasm of maturing and hypertrophic and, to a lesser extent, proliferating and degenerating chondrocytes; it was strongly positive in matrix vesicles, at the periphery of calcification nodules, and at the periphery of calcified matrix. In bone, the immunoreaction was especially strong along the peripheral membrane of the osteoblasts, in the interfibrillary spaces of the osteoid border, in matrix vesicles and in the peripheral zone of the calcification nodules. The central zone of the nodules, the fully calcified matrix and most of the intracellular membranes were negative in both cartilage and bone. These results confirm the presence of choline-containing phospholipids in early areas of calcification, including matrix vesicles. They also show that the intracellular membrane phospholipids are not accessible to the antibody, possibly because they are masked by other substances. These are not proteoglycans, because their enzymatic digestion does not increase or modify the reactivity of MC22-33F MAb. In spite of this limitation, MC22-33F MAb offers considerable advantages in the study of the calcification process, because the positive immunoreaction of the calcifying bone matrix, and the negativity of calcified matrix, confirm without doubt that phospholipids have an active role in biological calcification.
authors.affiliation: Department of Experimental Medicine and Pathology, University La Sapienza, Rome, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Bonucci
authors.forename: G
authors.initials: G
authors.lastname: Silvestrini
authors.forename: P
authors.initials: P
authors.lastname: Mocetti
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D000911:Antibodies, Monoclonal / Q000032:analysis*; D001842:Bone and Bones / Q000737:chemistry* / Q000648:ultrastructure; D003338:Corpus Luteum / Q000737:chemistry; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D006132:Growth Plate / Q000737:chemistry* / Q000648:ultrastructure; D007150:Immunohistochemistry; D016253:Microscopy, Immunoelectron; D010713:Phosphatidylcholines / Q000032:analysis; D010714:Phosphatidylethanolamines / Q000032:analysis; D010743:Phospholipids / Q000032:analysis* / Q000276:immunology; D051381:Rats
chemical_list: D000911:Antibodies, Monoclonal; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D010743:Phospholipids; C026508:phosphatidyldimethylethanolamine