Large-scale Early in vitro Response to Actinobacillus actinomycetemcomitans Suggests Superantigenic Activation of T-cells

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Abstract
The mode of T-cell response to Actinobacillus actinomycetemcomitans is largely unknown. The present study sought to investigate the hypothesis that A. actinomycetemcomitans expresses superantigens, capable of antigen-non-specific T-cell activation. To that end, peripheral blood mononuclear cells were stimulated with A. actinomycetemcomitans, and T-cell expression of the early activation marker, CD69, was determined by flow cytometry. Results showed that A. actinomycetemcomitans activated a large number of T-cells with magnitude similar to that of staphylococcal enterotoxin superantigens. A. actinomycetemcomitans sonicate preferentially activated T-cells expressing Vβ5.1 and Vβ8, while the extracellular preparation activated Vβ5.1+, Vβ8+, and Vβ12 + T-cells. T-cell response to A. actinomycetemcomitans was observed in the presence of autologous, as well as heterologous, antigen-presenting cells, suggesting a MHC-non-restricted response. Thus, the in vitro response to A. actinomycetemcomitans is characterized by large-scale T-cell activation in a Vβ-specific and MHC-non-restricted manner, consistent with the involvement of superantigens.