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RESEARCH PRODUCT

Concentration-dependent T cell activation by different types of proteins

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We investigated the concentration-dependent stimulation of T cells by different human proteins. Quantitative changes in the extent of activation, as well as qualitative changes within the type of activation, were measured. At low, physiological concentrations of extracellular human proteins (0.2 µg/ml), CD4 and CD8 T lymphocytes were suppressed. In contrast, at high protein concentrations (2 mg/ml), CD4 T cells were suppressed, but we also observed a concurrent increase in the level of CD8 T cell activation. Our results are consistent with the phenomenon of cross-presentation, whereby the addition of intracellular proteins leads to the activation of both CD4 and CD8 T cells. Further addition of a high concentration of extracellular proteins creates a density gradient across the cell membrane, thus also contributing to the rising protein concentrations within the cell. Consequently, CD8 lymphocyte activation occurs when extracellular proteins are added at high concentrations.