Subpopulation Composition and Activation of T Lymphocytes during Coculturing with Mesenchymal Stromal Cells in Medium with Different O2 Content

The concentration of O₂ during coculturing practically did not affect the subpopulation composition of T lymphocytes (CD3⁺/CD4⁺, CD3⁺/CD8⁺, CD3⁺/CD16⁺/CD56⁺ T cells) under conditions of PHA-induced activation. Coculturing with mesenchymal stromal cells (MSC) led to a significant decrease in the ratio of lymphocytes carrying activation markers (CD3⁺/CD25⁺ and CD3⁺/HLA-DR⁺) and increase in the number of CD3⁺/CD16⁺/CD56⁺ T cells. The percent of activated HLA-DR⁺ T cells in a heterotypic culture with MSC at 5% O₂ was much lower than that observed under normal conditions of culturing (20% O₂). Our results suggest that antigen presentation by T lymphocytes due to HLA-DR expression can be reduced in the target tissues at low concentration of O₂, while the interaction between allogeneic MSC probably contributes to more significant inhibition of the immune response.