BACKGROUND: Proximal tubular epithelial cells express a surface C3-convertase activity which induces C fixation and insertion of the C5b-9 membrane attack complex (MAC) into the cell plasma membrane. The physiopathological consequences of this phenomenon are unknown. METHODS: The effect of C fixation on the production of inflammatory mediators by human proximal tubular epithelial cells in culture was explored. RESULTS: Proximal tubular epithelial cells incubated with a sublytic amount of normal human serum as a source of C, but not with heat-inactivated human serum, showed a time-dependent calcium influx and a concomitant release of 14C-arachidonic acid (14C-AA). Eicosanoid synthesis following the arachidonic acid mobilization was studied as prostaglandin E2 release. Mg2+/EGTA, which did not prevent C activation by the C3-convertase, and p-bromodiphenacyl bromide a phospholipase A2-inhibitor, inhibited mobilization of 14C-AA. These results suggest the activation of an extracellular Ca(2+)-dependent, phospholipase A2. Complement fixation was associated with the synthesis of proinflammatory cytokines such as IL-6 and TNF-alpha. Experiments with C6-deficient sera indicated that the release of 14C-AA and the production of cytokines were dependent on the insertion of the terminal components of complement in the plasma membrane. Indeed, the reconstitution of normal haemolytic activity of C6-deficient sera with purified C6 restored also the release of 14C-AA and the production of cytokines. CONCLUSIONS: In vitro complement activation on the proximal tubular cell surface triggers the generation of proinflammatory mediators, which may potentially contribute to the pathogenesis of tubulointerstitial injury.
BACKGROUND: Proximal tubular epithelial cells express a surface C3-convertase activity which induces C fixation and insertion of the C5b-9 membrane attack complex (MAC) into the cell plasma membrane. The physiopathological consequences of this phenomenon are unknown. METHODS: The effect of C fixation on the production of inflammatory mediators by human proximal tubular epithelial cells in culture was explored. RESULTS: Proximal tubular epithelial cells incubated with a sublytic amount of normal human serum as a source of C, but not with heat-inactivated human serum, showed a time-dependent calcium influx and a concomitant release of 14C-arachidonic acid (14C-AA). Eicosanoid synthesis following the arachidonic acid mobilization was studied as prostaglandin E2 release. Mg2+/EGTA, which did not prevent C activation by the C3-convertase, and p-bromodiphenacyl bromide a phospholipase A2-inhibitor, inhibited mobilization of 14C-AA. These results suggest the activation of an extracellular Ca(2+)-dependent, phospholipase A2. Complement fixation was associated with the synthesis of proinflammatory cytokines such as IL-6 and TNF-alpha. Experiments with C6-deficient sera indicated that the release of 14C-AA and the production of cytokines were dependent on the insertion of the terminal components of complement in the plasma membrane. Indeed, the reconstitution of normal haemolytic activity of C6-deficient sera with purified C6 restored also the release of 14C-AA and the production of cytokines. CONCLUSIONS: In vitro complement activation on the proximal tubular cell surface triggers the generation of proinflammatory mediators, which may potentially contribute to the pathogenesis of tubulointerstitial injury.
Authors: Eivind O Samstad; Nathalie Niyonzima; Stig Nymo; Marie H Aune; Liv Ryan; Siril S Bakke; Knut T Lappegård; Ole-Lars Brekke; John D Lambris; Jan K Damås; Eicke Latz; Tom E Mollnes; Terje Espevik Journal: J Immunol Date: 2014-02-19 Impact factor: 5.422