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At least 1,621 records · Page 90Linked to original sources
PubMed1982

Functional active complement components secreted by guinea pig peritoneal macrophages.

In our studies on complement secretion functional C1, C4, C2, C3, P, D and B were clearly identified in the same cultures. Functional assays did not allow the detection of C5 to C9. Spontaneous C3 activation occurred at a very low level in culture supernatants. The responsible enzyme was identified as a metallo-enzyme. Upon addition of antibody-coated sheep erythrocytes (EA) to culture supernatant it was possible to induce C3 activation as indicated by the apparent formation of EAC1423. Zymosan was also able to activate C3 in culture supernatant after addition of purified functional factor B indicating efficient cooperation of factors of the alternative pathway. Thus in this in vitro system macrophages not only provide C3 but also all factors for spontaneous and induced C3 activation. If these secretory functions reflect in vivo properties of macrophages, our results may indicate that C3 and its activating systems are most relevant for local cooperation between macrophages and the complement system in inflammation and antimicrobial defense. Therefore availability of these essential factors at any time is secured by local production.

Animals↗
PubMed1983

Schistosoma mansoni: complement activation in human and rodent sera by living parasites of various developmental stages.

Living Schistosoma mansoni of various developmental stages were studied with respect to their ability to activate the complement system in sera of humans, mice and rats. Immunofluorescence assays demonstrated that binding of human C3 occurred on fresh schistosomula as well as on schistosomula prepared from mouse lymph-nodes or lungs and on adult schistosomes. However, rodent C3 was deposited only on fresh schistosomula. Deposition of human C3 on the worms' surface required activation of the complement system. The alternative pathway was shown to be involved in deposition of human C3 on schistosomes of all ages, whereas activation of the classical pathway was demonstrable only with fresh schistosomula. Immunoelectrophoretic studies demonstrated a dose-dependent cleavage of human C3 and conversion of factor B by living adult schistosomes. The results demonstrate that the ability of living schistosomes to activate complement in vitro is dependent not only on their development stage but also on the species of the serum.

Animals↗
PubMed1999

Mechanism of complement-dependent haemolysis via the lectin pathway: role of the complement regulatory proteins.

Mannan-binding lectin (MBL) is an acute phase protein which activates the classical complement pathway at the level of C4 and C2 via two novel serine proteases homologous to C1r and C1s. We recently reported that haemolysis via this lectin pathway requires alternative pathway amplification. The present experiments sought to establish the basis for this requirement, and hence focused on the activity and regulation of the C3 convertases. Complement activation was normalized between the lectin and classical pathways such that identical amounts of bound C4 and of haemolytically active C4,2 sites were present on the indicator cells. Under these conditions, there was markedly less haemolysis, associated with markedly less C3 and C5 deposited, via the lectin pathway than via the classical pathway, particularly when alternative pathway recruitment was blocked by depletion of factor D. Lectin pathway activation was associated with enhanced binding in the presence of MBL of complement control proteins C4bp and factor H to C4b and C3b, respectively, with decreased stability of the C3-converting enzyme C4b,2a attributable to C4bp. Immunodepletion of C4bp and/or factor H increased lectin pathway haemolysis and allowed lysis to occur in absence of the alternative pathway. Thus, the lectin pathway of humans is particularly susceptible to the regulatory effects of C4bp and factor H, due at least in part to MBL enhancement of C4bp binding to C4b and factor H binding to C3b.

Animals↗