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Isolation of a new superantigen with potent mitogenic activity to murine T cells from Streptococcus pyogenes
E Nemoto1, H Rikiishi, S Sugawara
1Department of Microbiology, Tohoku University School of Dentistry, Sendai Japan.
Abstract:
A mitogenic substance on murine lymphocytes was detected in the culture supernate of Streptococcus pyogenes type 12 strain. This substance had a molecular weight of 28,000 and pI 9.2, and was designated as S. pyogenes mitogen (SPM). The proliferative response of C3H/HeN spleen cells began at 1 ng ml-1 and reached a maximal response at 100 ng ml-1 of SPM for 4 days culture. Anti-Thy 1.2 mAb and complement-treated spleen cells abrogated the proliferative response to any dose of SPM. Although the anti-major histocompatibility complex class 1 mAbs had no blocking effect on proliferation by SPM, this proliferation was substantially inhibited by the addition of either anti-I-A or anti-I-E mAb, and complete inhibition was produced by the addition of both mAbs. Fixed antigen-presenting cells still induced T cell proliferation by SPM. A significant expansion of T cells bearing V beta 13 T-cell receptor was observed up to 73% among the Thy 1.2+ cells in cultures stimulated with SPM, indicating expansion in a V beta-specific manner. Immunoblotting of IEF-separated proteins showed that anti-streptococcal pyrogenic exotoxin (SPE) C reacted with a protein of pI 6.9 and anti-SPEB did not show any reactivity. SPEA was reported to expand V beta 8.1 and 8.2 bearing murine T cells, and SPM did not. SPM also exhibited potent mitogenic activity on human T cells and V beta 21+ T cells were selectively expanded. These results lead to the conclusion that SPM was neither SPEA, B nor C, but a new protein belonging to a group of streptococcal superantigens with activity on not only human but also murine lymphocytes.
Insights
A novel Streptococcus pyogenes mitogen (SPM) was identified, stimulating both human and murine lymphocytes. This superantigen selectively expands specific T cell receptor V beta chains, distinct from known streptococcal pyrogenic exotoxins.
Area of Science:
- Immunology
- Microbiology
- Molecular Biology
Background:
- Streptococcus pyogenes produces various exotoxins that modulate the immune system.
- Superantigens are potent activators of T cells, leading to massive cytokine release and immune dysregulation.
Purpose of the Study:
- To isolate and characterize a novel mitogenic substance from Streptococcus pyogenes type 12.
- To investigate the mechanism of T cell activation and specificity of this substance.
Main Methods:
- Isolation and purification of the mitogenic substance (SPM).
- Assays for murine and human lymphocyte proliferation.
- Flow cytometry using monoclonal antibodies against T cell markers and T cell receptor V beta chains.
- Immunoblotting to compare with known streptococcal pyrogenic exotoxins (SPEA, SPEB, SPEC).
Main Results:
- A mitogen, S. pyogenes mitogen (SPM), with MW 28,000 and pI 9.2, was isolated.
- SPM induced proliferation of murine and human T cells in a dose-dependent manner.
- SPM selectively expanded T cells expressing specific T cell receptor V beta chains (V beta 13 in mice, V beta 21 in humans).
- SPM's activity was dependent on MHC class II molecules and distinct from SPEA, SPEB, and SPEC.
Conclusions:
- SPM is a novel streptococcal superantigen with potent mitogenic activity on lymphocytes.
- SPM exhibits distinct V beta specificity compared to other known streptococcal superantigens.
- SPM represents a new class of superantigens with implications for understanding T cell activation and pathogenesis.