Processing of C5a by human polymorphonuclear leukocytes

Abstract

Uptake of human C5a by neutrophils was monitored in vitro using both 125 I-labeled and unlabeled C5a. The ligand was internalized by the cells in a dose-dependent manner and maximal binding/uptake was observed after 5 min of incubation. Neutrophils were incubated with labeled C5a and the cytosol and supernatant were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography. C5a degradation products were primarily observed in the supernatant, whereas most of the protein remained intact in the cytosol even after 60 min of incubation. Cytosol from neutrophils incubated for 20 min with unlabeled C5a was examined by radioimmunoassay and found to contain antigenically intact C5a and retained the ability to induce a neutrophil (shape change) response. The functional activity of C5a recovered from the cytosol was inhibited by antibodies to either C5a or the C5a receptor (CD88). This data supports our hypothesis that although C5a is internalized it remains antigenically intact and functionally active inside the cell and is primarily degraded extracellularly.

Complement activation predicts negative outcomes in COVID-19: The experience from Northen Italian patients.

“…It is worth noting that the levels of sC5b-9 appear to be a more reliable marker of in vivo complement activation being high in a few patients whose C5a levels fell within the normal range. This finding is consistent with data in our previous studies [ 7 , 8 ] and can be explained by the fact that soluble sC5b-9 is a more stable complex that remains in the fluid phase in comparison with anaphylatoxin C5a which can be cleared and recycled by C5a receptors with different kinetics [ 51 , 52 ].…”

Role of complement C5a in mechanical inflammatory hypernociception: potential use of C5a receptor antagonists to control inflammatory pain

“…Thus, although the recruitment of neutrophils is essential for the genesis of inflammatory hypernociception, in the absence of their activation by C5a, hypernociception is not triggered even though they are present in the inflammatory focus. It is possible that C5a generated in the inflammatory focus activates the recruited neutrophils to produce permissive hypernociceptive products yet to be determined ( Hetland et al , 1998 ; Castellheim et al , 2005 ). For instance, there is evidence that the activation of neutrophils leads to the production of prostaglandins and of 15‐HETE, which also shows a hypernociceptive effect ( Levine et al , 1985 ; Akama et al , 1990 ; Cunha et al , unpublished observations).…”

“…It is one of the most potent inflammatory peptide mediators, and its biological effects result in binding to its G‐protein‐coupled receptor (C5aR1) present in inflammatory cells, such as neutrophils, eosinophils and monocytes ( Chenoweth and Hugli, 1978 ; Gerard et al , 1989 ; Werfel et al , 1992 ). C5a is a potent neutrophil chemoattractant and induces an increase in oxidative burst, phagocytosis and release of granule enzymes by these cells ( Hetland et al , 1998 ).…”