Calcium-dependent protection from complement lysis in Naegleriafowleri amebae

Abstract

Pathogenic Naegleria fowleri amebae are resistant to the lytic effects of serum complement. The presence of surface glycoproteins or removal of the membrane attack complex (MAC) of complement from the cell surfaceby vesiculation serve to protect the amebae from complement lysis. T he specific mediators important in stimulating complement resistance are not defined. These studies were undertaken to examine the effect of Ca2+ ions in initiating complement resistance of N. fowleri in contrast to non-pathogenic complement-sensitive N. gruberi. Chelation of extracellular calcium with ethylene glycol tetraacetic acid (EGTA) or chelation of intracellular calcium with 1,2-bis-(O-Aminophenoxy) ethane-N,N,N,N tetraacetic acid tetra (acetoxymethyl) ester (BAPTA-AM) increased complement lysis ofN. fowleri . Chelation of calcium ions did not affect complement sensitivity of N. gruberi. Increased lysis of ionomycin-treated N. fowleri was detected after exposure to serum complement, suggesting that a threshold level of Ca2+ mediates complement resistance before survival mechanisms are overwhelmed and lysis occurs. A differential influx of Ca2+ ions occurred in fura-2 labeled N. fowleri after deposition of complement component C9 to form the MAC complex on the cell surface in comparison to N. gruberi. These studies suggest that Ca2+ ions influence complement resistance in N. fowleri but do not play a role in altering the sensitivity of N. gruberi to complement.