Cs. Mintz et al., ANTIBODY-INDEPENDENT BINDING OF COMPLEMENT COMPONENT C1Q BY LEGIONELLA-PNEUMOPHILA, Infection and immunity, 63(12), 1995, pp. 4939-4943
Incubation of Legionella pneumophila Philadelphia 1 in normal human se
rum depleted of either classical-pathway component C1q or alternative-
pathway component factor B resulted in activation of the complement sy
stem. Experiments focused on the role of the classical pathway in comp
lement activation revealed that legionellae bound C1q independently of
antibody. Purified preparations of L. pneumophila major outer membran
e protein but not serogroup 1 lipopolysaccharide bound C1q independent
ly of antibody. This suggests that antibody-independent binding of C1q
by L. pneumophila can result in activation of the classical pathway i
n normal human serum and that major outer membrane protein may be a C1
q acceptor on the L. pneumophila cell surface.