Interaction of pathogenic and nonpathogenic Entamoeba histolytica with human complement
Reed, S.L.; Gault, M.; Gillin, F.D.; Gigli, I.; Braude, A.I.; Curd, J.G.; Sargeaunt, P.G.
Archivos de Investigacion Medica 18(2): 141-149
1987
ISSN/ISBN: 0066-6769 PMID: 2889433 Document Number: 287044
Resistance to complement-mediated lysis may be an important virulence mechanism for invasive strains of E. histolytica. Each of thirty-four isolates from asymptomatic patients were rapidly lysed (66.8 .+-. 12.1 percent) by normal human serum (NHS) while strains from 23 patients with invasive disease were resistant to NHS (3.2 .+-. 5.5 percent lysis) and immune sera (9.8 .+-. 11.3 percent). Maintenance of complement resistance of pathogenic strains appeared to be dependent on growth conditions as two complement resistant strains became sensitive during the process of axenization. Activation of the alternative pathway was important in the lysis of nonpathogenic strains as demonstrated by lysis in NHS (59.3 .+-. 4.5 percent), NHS + 5 mM EGTA (60.9 .+-. 15.6 percent) as well as C4-deficient guinea pig serum (71.0 .+-. 9.1 percent) and C2-deficient human serum (70.7 percent) but not by NHS + 5 mM EDTA. In contrast, pathogenic strains were resistant to lysis by both classical and alternative pathways. Both complement-sensitive and complement-resistant strains depleted complement comparably as assessed by CH50, C3, C7, and C5-9 hemolytic activities. In addition, more than 98 percent of the C4 hemolytic activity was depleted by both pathogenic and nonpathogenic strains, indicating that classical pathway activation occurs even though it is not necessary for lysis. These studies demonstrate that pathogenic strains of E. histolytica do activate complement but are able to evade complement-mediated killing.