ALTERNATIVE PATHWAY ACTIVATION OF COMPLEMENT BY CULTURED HUMAN PROXIMAL TUBULAR EPITHELIAL-CELLS

Human proximal tubular epithelial cells (PTEC) incubated with normal h uman serum (NHS) were found to fix on their surface C3, properdin, ter minal complement components and C5b-9 MAC neoantigen, but not Clq and C4, by immunofluorescence. Complement fixation was abrogated if PTEC w ere incubated with EDTA-treated NHS or C3-deficient human serum, but n ot with Mg EGTA-treated NHS or C1q-deficient human serum, showing the prevalent activation of the alternative pathway of complement. This ev ent was followed by marked cytoskeleton alterations with disruption of the actin cortical network, redistribution of actin throughout the cy toplasm and formation of blebs, and by cell cytolysis. In addition, su peroxide anion and hydrogen peroxide production and chemiluminescence response were detected in consequence of MAC insertion on PTEC plasma membrane. The dependency on MAC of the observed biological effects of complement fixation on PTEC surface was shown by using sera selectivel y deficient of terminal components of complement (C6 or C8), and there fore unable to form the C5b-9 MAC, and by restoring the ability to for m MAC after addition of purified C6 or C8. The possible pathogenetic r elevance of these observations in tubulointerstitial injury occurring in patients with complementuria due to non-selective proteinuria, is d iscussed.