Entamoeba histolytica inhibits the respiratory burst of polymorphonuclear leukocytes

Since toxic oxygen metabolites generated during the respiratory burst of polymorphonuclear neutrophils (PMNs) constitute one of the most potent microbicidal mechanisms of PMNs, we evaluated the in vitro capacity of E histolytica to trigger the respiratory burst of human PMNs using a luminol-enhanced chemiluminescence assay a highly virulent strain of E. histolytica (HM1-IMSS) and a less virulent one (HK9-NIH) were incubated with PMNs at 4:1, 2:1 and 1:1 PMN:amoebae ratios. We have observed that the HM1-IMSS strain of E. histolytica do not induce PMN chemiluminescence as compared with zymosan (4.57.1.1 vs 106.5.11.3 mV/2 x 10(5) PMN, p less than 0.001). More importantly, the neutrophil oxidative response decreased progressively when the concentration of amoebae in the reaction mixture increased. When PMNs were challenged with zymosan in the presence of amoebae, the response was abrogated. These results suggest that E. histolytica inhibits the respiratory burst of PMNs. This represents a unique survival tactic and may contribute to the pathogenesis of amebiasis.