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Induction of complement resistance in cloned pathogenic Entamoeba histolytica
C Hamelmann1, B Foerster, G D Burchard
1Bernhard Nocht Institute for Tropical Medicine, Hamburg, Federal Republic of Germany.
Abstract:
The lytic effect of complement activated through the alternative pathway (AP) was studied on pathogenic and nonpathogenic Entamoeba histolytica recently isolated from stool samples. Recent nonpathogenic isolates were nearly unaffected by exposure to AP whereas recent pathogenic stool isolates were highly susceptible to AP dependent complement-mediated lysis. Complement susceptible pathogenic stool isolates developed complement resistance in vivo during hamster liver passage and in vitro during cultivation in the presence of increasing concentrations of normal human serum (NHS). Since a clone of pathogenic HM-1:IMSS which initially was highly susceptible also acquired complement resistance during cultivation in the presence of NHS, it is concluded that complement resistance was caused by induction rather than by selection alone. Because cultivation in the presence of heat-inactivated NHS did not affect complement susceptibility of the cloned HM-1:IMSS, complement activation itself might induce complement resistance in pathogenic E. histolytica.
Insights
Pathogenic Entamoeba histolytica, unlike nonpathogenic strains, is susceptible to alternative pathway (AP) complement lysis. Complement resistance develops through induction, not just selection, potentially triggered by complement activation itself.
Area of Science:
- Immunology
- Infectious Diseases
- Parasitology
Background:
- Entamoeba histolytica is a protozoan parasite causing amoebiasis.
- The alternative pathway (AP) of the complement system plays a role in innate immunity against pathogens.
Purpose of the Study:
- To investigate the susceptibility of pathogenic and nonpathogenic Entamoeba histolytica to AP-mediated lysis.
- To determine the mechanisms by which Entamoeba histolytica develops resistance to complement.
Main Methods:
- Testing lysis of Entamoeba histolytica isolates using AP-dependent complement.
- Inducing complement resistance in vitro by cultivating parasites in normal human serum (NHS).
- Assessing complement resistance in vivo through hamster liver passage.
Main Results:
- Nonpathogenic Entamoeba histolytica isolates showed minimal susceptibility to AP lysis.
- Pathogenic isolates were highly susceptible to AP-mediated lysis, but developed resistance during in vivo and in vitro cultivation.
- A pathogenic clone (HM-1:IMSS) acquired resistance when cultured with NHS, suggesting induced resistance.
Conclusions:
- Complement resistance in pathogenic Entamoeba histolytica is primarily induced rather than solely selected.
- Complement activation itself may trigger the development of complement resistance in Entamoeba histolytica.