The cDNA sequence and the deduced amino acid sequence of the Mr 34,000 C-terminal fragment of Xenopus laevis complement component C3 are presented. The sequence of Xenopus C3 has 57% nucleotide identity to the corresponding sequence of human C3 and approximately 49% amino acid identity to C3 from human, mouse, and rabbit. The Xenopus C3 sequence shows clusters of high and of low similarity to t...

An intracellular complement system (ICS) has recently been described in immune and nonimmune human cells. This system can be activated in a convertase-independent manner from intracellular stores of the complement component C3. The source of these stores has not been rigorously investigated. In the present study, Western blotting identified a band corresponding to C3 in freshly isolated human p...

Staphylococcus aureus can cause a variety of acute and chronic diseases. The ability of S. aureus to cause persistent infections has been linked to its ability to evade or inactivate host immune responses. We have identified a secreted 19-kDa protein produced by S. aureus that binds to the complement protein C3. N-terminal sequencing of this protein identified it as the extracellular fibrinogen...

The human pathogen Staphylococcus aureus produces several complement-evasion molecules that enable the bacterium to withstand the host immune response. The human-specific staphylococcal complement inhibitor (SCIN) blocks the central C3 convertase enzymes that trigger critical complement functions, such as C3b deposition, phagocytosis, and C5a generation. SCIN effectively blocks the conversion o...

The complement system plays an important role in eliminating invading pathogens. Activation of complement results in C3b deposition (opsonization), phagocytosis, anaphylatoxin (C3a, C5a) release, and consequently cell lysis. Moraxella catarrhalis is a human respiratory pathogen commonly found in children with otitis media and in adults with chronic obstructive pulmonary disease. The species has...

We have previously provided evidence that suggests that exposure of cryostat skin sections to normal human serum (NHS) results in the antibody-independent Clq binding to cytoplasmic structures of various cell types, leading to classical complement pathway activation as evidenced by cytoplasmic C3 deposition. In the present study, we have employed immunoelectronmicroscopic methods to clarify the...

PURPOSE To determine if the progression of age-related macular degeneration (AMD) is associated with complement activation in the eye. METHODS Immunohistochemistry and ELISAs were used to determine the distribution, concentration, and activation of the alternative pathway complement proteases factor B (FB) and factor D (FD) and the central complement protein C3 in genotyped human postmortem d...

In a strategy to specifically target complement inhibitors to sites of complement activation and disease, recombinant fusion proteins consisting of a complement inhibitor linked to a C3 binding region of complement receptor (CR) 2 were prepared and characterized. Natural ligands for CR2 are C3 breakdown products deposited at sites of complement activation. Fusion proteins were prepared consisti...

To assess the contribution of complement to respiratory immunity in the context of a natural bacterial infection, we used mice genetically deficient in complement components and the murine pathogen Bordetella bronchiseptica. Complement component C3 was not required for the control of bacterial infection or for the generation of infection-induced protective immunity. However, C3-deficient (C3(-/...