Infect Immun, February 1998, p. 399-405, Vol. 66, No. 2
Department of Molecular Genetics and
Microbiology, University of New Mexico, Albuquerque, New
Mexico,1 and
Institute of Pathology,
Case Western Reserve University, Cleveland, Ohio2
Received 9 June 1997/Returned for modification 30 July
1997/Accepted 3 November 1997
The alternative complement pathway (ACP) functions as a
surveillance mechanism by which microorganisms are opsonized with C3b
in the absence of specific antibodies. The effectiveness of the ACP
relies on its ability to distinguish self from non-self. This
recognition function is mediated by C3 regulatory proteins including
serum factor H, membrane cofactor protein (MCP), and membrane
decay-accelerating factor (DAF). H activity against bound C3b can be
increased by host components such as sialic acid and decreased by
microbial polysaccharides. DAF and MCP may also recognize cell surface
changes such as the presence of viral glycoproteins, since some
virus-infected and tumor cells activate the ACP. In the present study,
liposomes containing wild-type and mutant Salmonella minnesota lipopolysaccharide (LPS) were tested for ACP activation in serum. LPS-containing liposomes with bound C3b were then tested for
their susceptibility to C3 convertase regulation by H and membrane DAF
and for the sensitivity of their bound C3b to the cofactor activity of
H. The results indicate that while the shortest mutant, Re595 LPS, did
not induce ACP activation, R7 LPS containing an additional disaccharide
did. This activation was poorly regulated by DAF but was inhibited by
H. The regulatory activity of H for liposome-bound C3b, however,
decreased when LPS of greater polysaccharide size was present in the
membrane. In contrast the ACP activation induced by the phospholipid
phosphatidylethanolamine was effectively inhibited by DAF but only
poorly inhibited by H.
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Complementary Recognition of Alternative Pathway
Activators by Decay-Accelerating Factor and Factor H

*
Corresponding author. Mailing address: Department of
Molecular Genetics and Microbiology, University of New Mexico School of
Medicine, Albuquerque, NM 87131. Phone: (505) 272-5768. Fax: (505)
272-6029. E-mail: cmold{at}medusa.unm.edu.
Present address: Department of Medicine, University of Colorado
Health Sciences Center, Denver, CO 80262.
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