The opsonic fragment of the third component of human complement (C3).

Abstract

Human peripheral blood phagocytes ingest Escherichia coli 026:B6 lipopolysaccharide (LPS)-coated paraffin oil droplets containing Oil red O only if fresh serum deposits C3 on the surfaces of the particles (opsonizes them), by reactions involving the properdin system. The rate of binding of purified [125-I]C3 in serum to LPS-coated particles correlated precisely with the rate of acquisition of ingestibility assayed spectrophotometrically. Once opsonized, LPS-coated particles remained fully ingestible and retained fixed [125-I]C3 radioactivity even after exposure to extremes of temperature, pH, ionic strength, phospholipases, urea or guanidine, some nonionic and ionic detergents, and organic solvents. Trypsin, human conglutinogen-activating factor, another heat-stable activity found in human serum, and sodium dodecyl sulfate removed radioactivity and diminished ingestibility of the opsonized particles. Alkylation, reduction plus alkylation and F(ab')2 from anti-C3 blocked ingestibility but did not alter particle-bound radioactivitymelectrophoretic and tryptic peptide autoradiographic analysis of dodecyl sulfate eluates of opsonized particles, cleansed of many contaminating proteins by boiling with 2 M NaCl (yet still opsonized), revealed that the polypeptide with C3-derived radioactivity had a mol wt of approximately 140,000 and was composed of 70,000 mol wt subunits linked by disulfide bonds. Immunochemical analysis and comparison of the peptide structure of the eluate with that of C3 indicated that the opsonic fragment is not the fragment defined as C3b but a smaller derivative of C3.

Pathogenesis of Foreign Body Infection: Description and Characteristics of an Animal Model

“…In contrast to these observations for the early stage of infection, opsonic coating of the infecting microorganism S. aureus strain Wood 46 -presumably by functional C3 [46] -was markedly decreased during the course of the infection. This observation is open to at least two interpretations.…”

On the binding of complement to solid artificial surfaces in vitro

“…to surfaces. In other studies, strong covalent associations between albumin and C3-fragments have been reported [47,48]. Furthermore, IgG and C1q are transiently detectable at the Au-MG surfaces after contact with NHS [27], and IgG enhances the alternative pathway activation via the classical pathway [3].…”

The sequential appearance of Ia-like antigens and two different complement receptors during the maturation of human neutrophils.

“…There is similar complexity in the in vivo reactions involving immune complex-bound C3b. It is well known that when the immune complexes are sheep erythrocytes (EAC), the cell-bound C3b cleavage product, the C3d fragment, has little or no opsonic activity (2,26,27). However, under normal circumstances in vivo, C3-coated bacteria and yeast are the more usual fare of phagocytes, and erythrocyte target cells are more likely to be handled instead by lysis with natural antibodies and complement.…”

“…Many strains of bacteria and yeast spontaneously trigger the alternative pathway of C activaton and as a result become coated with C3b that is subsequently cleaved by C3b inactivator. However, in contrast to sheep cell membranes, Stossel et al (26) have shown that bacterial cell wallderived lipopolysaccharide-coated paraffin oil particles retain an opsonically active form of C3 despite prolonged incubation with whole serum. FurthermOre, Fearon and Austen (28) have demonstrated that yeast cell wall-derived zymosan surfaces differ from sheep erythrocyte membranes in that alternative pathwayderived C3b is bound in such a way that it is relatively resistent to cleavage by C3b inactivator.…”