Antibody-independent binding of complement component C1q by Legionella pneumophila.
Incubation of Legionella pneumophila Philadelphia 1 in normal human serum depleted of either classical-pathway component C1q or alternative-pathway component factor B resulted in activation of the complement system. Experiments focused on the role of the classical pathway in complement activation revealed that legionellae bound C1q independently of antibody. Purified preparations of L. pneumophila major outer membrane protein but not serogroup 1 lipopolysaccharide bound C1q independently of antibody. This suggests that antibody-independent binding of C1q by L. pneumophila can result in activation of the classical pathway in normal human serum and that major outer membrane protein may be a C1q acceptor on the L. pneumophila cell surface.
Mintz
C S
CS
Department of Microbiology and Immunology, University of Miami School of Medicine, Florida 33101, USA.
Arnold
P I
PI
Johnson
W
W
Schultz
D R
DR
D000907:Antibodies, Bacterial / Q000276:immunology; D001426:Bacterial Proteins; D015922:Complement C1q / Q000276:immunology*; D003170:Complement Pathway, Alternative; D003171:Complement Pathway, Classical; D006801:Humans; D016952:Legionella pneumophila / Q000276:immunology*; D018272:Porins / Q000378:metabolism
D000907:Antibodies, Bacterial; D001426:Bacterial Proteins; D018272:Porins; C072453:major outer membrane protein, Legionella pneumophila; D015922:Complement C1q