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Externally disposed membrane polypeptides of intact and protease-treated Trypanosoma lewisi correlated with
Abstract:
Reproducing forms of Trypanosoma lewisi isolated from X-irradiated rats and adult forms from intact rats were not lysed by fresh mammalian sera. Treating parasites with trypsin or chymotrypsin, but not with neuraminidase, under conditions which did not impair viability rendered the parasites sensitive to lysis by rat, mouse, rabbit, and human sera. Serum from animal strains or humans genetically deficient in complement component C3, C5, or C6 did not lyse protease-treated parasites. The lytic factors in serum displayed the heat sensitivity and the Mg2+ requirement characteristic of the alternate complement pathway. Lysis was resolved into two phases, Mg2+-dependent binding of serum factors to parasites and subsequent C5-dependent, Mg2+-independent lysis. Allowing protease-treated parasites to readsorb host proteins did not block lysis by serum. Protease-treated parasites regenerated components which prevented complement-mediated lysis during 2 h in culture at 37 degrees C. This regeneration was inhibited by cycloheximide but not by tunicamycin. Ten major components were resolved in radioautographs of sodium dodecyl sulfate-polyacrylamide gels of extracts of radioiodinated intact cells. Protease treatment before radioiodination reduced the amount of radioactivity associated with these components disproportionately. Components with apparent molecular weights of 102,000, 88,000, and 47,000 were strongly labeled in intact cells, poorly labeled after enzyme treatment, and again labeled in cells that were cultured at 37 degrees C after enzyme treatment. Cycloheximide blocked the reappearance of these components on cultured cells. The presence of these three components was therefore correlated with resistance to complement-mediated lysis.
Insights
Trypanosoma lewisi parasites resist complement lysis until surface proteins are removed by proteases. These parasites regenerate protective components, suggesting a mechanism for evading the host immune system.
Area of Science:
- Immunology
- Parasitology
- Molecular Biology
Background:
- Trypanosoma lewisi parasites exhibit resistance to lysis by fresh mammalian sera.
- This resistance is crucial for parasite survival in the host bloodstream.
Purpose of the Study:
- To investigate the mechanisms underlying Trypanosoma lewisi resistance to complement-mediated lysis.
- To identify parasite surface components involved in evading host immune responses.
Main Methods:
- Parasite treatment with proteases (trypsin, chymotrypsin, neuraminidase) and subsequent serum lysis assays.
- Complement component analysis using serum from deficient animal strains.
- Analysis of parasite surface protein regeneration using cycloheximide and tunicamycin.
- Radioiodination and SDS-PAGE to identify and quantify surface proteins.
Main Results:
- Protease treatment (trypsin, chymotrypsin) sensitized parasites to lysis by various mammalian sera.
- Lysis involved the alternate complement pathway, requiring Mg2+ and complement components C3, C5, and C6.
- Protease-treated parasites regenerated resistance within 2 hours via cycloheximide-sensitive protein synthesis.
- Three specific surface proteins (102, 88, and 47 kDa) were identified as key to complement resistance.
Conclusions:
- Trypanosoma lewisi employs surface proteins to evade complement-mediated lysis.
- Parasite regeneration of these protective components is a key survival strategy.
- Targeting these specific surface proteins could offer new therapeutic avenues against trypanosomiasis.