Human alveolar macrophages synthesize active complement components C6, C7, and C8 in vitro.
We investigated whether serum-free human alveolar macrophage cultures synthesize active C6, C7, and C8. There was a significant binding of polyclonal anti-human C6 antibodies to agarose beads incubated with unstimulated macrophages for 24 or 48 h. Endotoxin stimulation of the macrophages was necessary for significant binding of polyclonal anti-C7 and anti-C8 antibodies to agarose beads co-cultured for 48 or 96 h. Two monoclonal antibodies (poly C9-MA and MCaE11) specific for a neoantigen of polymerized C9 in the terminal complement complex (TCC), bound to beads mainly incubated with endotoxin stimulated macrophages. The MCaE11 was more sensitive than the poly C9-MA in detecting the C9 neoantigen on beads incubated with the macrophages or human serum diluted 1:16. We thus conclude that human alveolar macrophages synthesize active C6, C7, and C9 that together with C5 and C9, assemble as the TCC on co-cultured agarose beads. Activation of the alternative pathway on the agarose with generation of fixed C3 and C5 convertases is a prerequisite for the subsequent generation of the TCC.
D000328:Adult; D003167:Complement Activation; D003183:Complement C6 / Q000096:biosynthesis*; D003184:Complement C7 / Q000096:biosynthesis*; D003185:Complement C8 / Q000096:biosynthesis*; D006801:Humans; D008264:Macrophages / Q000378:metabolism*; D011650:Pulmonary Alveoli / Q000166:cytology; D012685:Sepharose / Q000378:metabolism
D003183:Complement C6; D003184:Complement C7; D003185:Complement C8; D012685:Sepharose