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Separation of T-cell-stimulating activity from streptococcal M protein
B Fleischer1, K H Schmidt, D Gerlach
1First Department of Medicine, University of Mainz, Germany.
Abstract:
The superantigenic properties of M protein type 5 of Streptococcus pyogenes have been implicated as an important pathogenicity factor in streptococcal autoimmune diseases. Here we show that after a single purification step by affinity chromatography on immobilized albumin or fibrinogen, M protein has no mitogenic activity for T cells. We demonstrate that the superantigenicity of M proteins of type 5 and type 1 is due to contamination with the highly potent pyrogenic exotoxins of S. pyogenes in the range of 0.1 to 0.01%. These results raise a general caveat for work with these extremely active T-cell mitogens, because the mitogenicity of other streptococcal or staphylococcal proteins could be due to similar minute contamination with potent superantigens that are undetectable by any biochemical method but extremely effective in stimulating sensitive T cells.
Insights
Streptococcus pyogenes M protein
Area of Science:
- Microbiology
- Immunology
- Molecular Biology
Background:
- M protein of Streptococcus pyogenes is linked to autoimmune diseases.
- Its superantigenic properties are considered a key pathogenicity factor.
Purpose of the Study:
- To investigate the superantigenic activity of M protein.
- To determine the cause of T-cell mitogenicity in M protein preparations.
Main Methods:
- Purification of M protein using affinity chromatography.
- Assessing T-cell mitogenic activity of purified M protein.
- Quantifying potential contaminants.
Main Results:
- Purified M protein (types 5 and 1) showed no T-cell mitogenic activity.
- Superantigenicity was attributed to trace contamination (0.01–0.1%) with pyrogenic exotoxins.
- Contaminants were undetectable biochemically but highly potent T-cell stimulators.
Conclusions:
- The superantigenic activity of M protein is likely due to contaminant pyrogenic exotoxins.
- Minute contamination can significantly impact T-cell stimulation assays.
- Caution is advised when interpreting T-cell mitogenicity data for streptococcal and staphylococcal proteins.