Separation of T-cell-stimulating activity from streptococcal 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.