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Resistance of highly pathogenic Naegleria fowleri amoebae to complement-mediated lysis
L Y Whiteman1, F Marciano-Cabral
1Department of Microbiology and Immunology, Virginia Commonwealth University, Medical College of Virginia, Richmond, 23298-0678.
Abstract:
Weakly pathogenic and nonpathogenic Naegleria spp. are readily lysed by human and guinea pig complement. Highly pathogenic Naegleria fowleri are resistant to complement-mediated lysis. Electrophoretic analysis of normal human serum (NHS) incubated with pathogenic or nonpathogenic Naegleria spp. demonstrates that amoebae activate the complement cascade, resulting in the production of C3 and C5 complement cleavage products. To determine whether surface constituents play a role in resistance to complement lysis, trophozoites of Naegleria spp. were subjected to enzymatic treatments prior to incubation in NHS. Treatment of trophozoites with papain or trypsin for 1 h, but not with neuraminidase, increased susceptibility of highly pathogenic Naegleria fowleri to complement lysis. Treatment of trophozoites with actinomycin D or cycloheximide during incubation with NHS or pretreatment with various protease inhibitors for 4 h did not increase the susceptibility of N. fowleri amoebae to lysis. Neither a repair process involving de novo protein synthesis nor a complement-inactivating protease appears to account for the increased resistance of N. fowleri amoebae to complement-mediated lysis.
Insights
Highly pathogenic Naegleria fowleri resist complement lysis, unlike weaker strains. Surface protein removal with papain or trypsin increased susceptibility, suggesting these proteins contribute to Naegleria fowleri's resistance to complement-mediated lysis.
Area of Science:
- Immunology
- Microbiology
- Parasitology
Background:
- Complement-mediated lysis is crucial for host defense against pathogens.
- Naegleria spp. exhibit varying susceptibility to complement lysis, with pathogenic Naegleria fowleri being resistant.
- Pathogenic Naegleria fowleri activate the complement cascade but resist lysis.
Purpose of the Study:
- To investigate the role of surface constituents in Naegleria fowleri's resistance to complement-mediated lysis.
- To identify potential mechanisms of complement resistance in pathogenic Naegleria species.
Main Methods:
- Enzymatic treatment (papain, trypsin, neuraminidase) of Naegleria spp. trophozoites.
- Incubation of treated trophozoites with normal human serum (NHS).
- Assessment of complement-mediated lysis susceptibility.
- Inhibition studies with actinomycin D, cycloheximide, and protease inhibitors.
Main Results:
- Treatment with papain or trypsin significantly increased the susceptibility of pathogenic Naegleria fowleri to complement lysis.
- Neuraminidase treatment did not affect complement lysis susceptibility.
- Inhibition of protein synthesis or pre-incubation with protease inhibitors did not enhance lysis susceptibility.
- No evidence of a complement-inactivating protease or de novo protein synthesis for repair was found.
Conclusions:
- Surface proteins, potentially sensitive to papain and trypsin, play a significant role in the resistance of pathogenic Naegleria fowleri to complement-mediated lysis.
- The resistance mechanism does not appear to involve de novo protein synthesis or a secreted complement-inactivating protease.