ALTERNATIVE PATHWAY COMPLEMENT ACTIVATION INDUCES PROINFLAMMATORY ACTIVITY IN HUMAN PROXIMAL TUBULAR EPITHELIAL-CELLS

Background. Proximal tubular epithelial cells express a surface C3-con vertase activity which induces C fixation and insertion of the C5b-9 m embrane attack complex (MAC) into the cell plasma membrane. The physio pathological consequences of this phenomenon are unknown. Methods. The effect of C fixation on the production of inflammatory mediators by h uman proximal tubular epithelial cells in culture was explored. Result s. 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 C-14-arachidonic acid (C-14-AA). Eicosanoid synthesis follo wing the arachidonic acid mobilization was studied as prostaglandin E( 2) release; Mg2+/EGTA, which did not prevent C activation by the C3-co nvertase, and p-bromodiphenacyl bromide, a phospholipase A(2)-inhibito r, inhibited mobilization of C-14-AA. These results suggest the activa tion of an extracellular Ca2+-dependent, phospholipase A(2). Complemen t fixation was associated with the synthesis of proinflammatory cytoki nes such as IL-6 and TNF-alpha. Experiments with C6-deficient sera ind icated that the release of C-14-AA and the production of cytokines wer e dependent on the insertion of the terminal components of complement in the plasma membrane. Indeed, the reconstitution of normal haemolyti c activity of CG-deficient sera with purified C6 restored also the rel ease of C-14-AA and the production of cytokines. Conclusions. In vitro complement activation on the proximal tubular cell surface triggers t he generation of proinflammatory mediators, which may potentially cont ribute to the pathogenesis of tubulointerstitial injury.