Influence of oxygen concentration on T cell proliferation and susceptibility to apoptosis in healthy men and women.

INTRODUCTION: Much of what we know about the functioning of human T lymphocytes is based on the experiments carried out in atmospheric oxygen (O₂) concentrations, which are significantly higher than those maintained in blood. Interestingly, the gender differences in the activity of T cells and their susceptibility to apoptosis under different O₂ conditions have not yet been described. The aim of the study was to compare two main markers of lymphocyte function: proliferation capacity and ability to produce cytokines as well as their susceptibility to apoptosis under two different O₂ concentrations, between men and women.

MATERIALS AND METHODS: 25 healthy volunteers, both males (13) and females (12) were recruited to the study (mean age 25.48 ± 5.51). By using cytometry proliferation parameters of human CD4+ CD28+ cells or CD8+CD28+ cells in response to polyclonal stimulation of the TCR/CD3 complex at atmospheric (21%) and physiological (10%) O₂ concentrations using our modified dividing cell tracking technique (DCT) were analyzed as well as the percentages of apoptotic cells. We also determined the levels of IFN-γ, IL-2, IL-10 and IL-17A using Cytometric Bead Array Flex system in cell culture supernatants.

RESULTS: CD4+CD28+ and CD8+CD28+ cells from the whole study group were characterized by shorter time required to enter the first (G1) phase of the first cell cycle at 21% compared to 10% O₂. Both T cell populations performed significantly more divisions at 21% O₂. The percentages of dividing cells were also significantly higher at atmospheric O₂. Interestingly, data analysis by gender showed that male lymphocytes had similar proliferative parameters at both O₂ concentrations while female lymphocytes proliferate more efficiently (note from the author: we cannot say that lymphocytes proliferate faster, rather more effectively, because cells perform more divisions, which gives more percentage of offspring cells) at 21% oxygen. Compared to males, the female CD4+ cells showed increased susceptibility to apoptosis at both O₂ concentrations. No differences in the levels of cytokines regardless of gender and oxygen conditions were found.

CONCLUSIONS: We showed that in vitro female T cells (both CD4+ and CD8+ cells) are more sensitive than male lymphocytes to low O2 concentration as demonstrated by the decrease in their proliferation dynamics. The effect does not depend on increased apoptosis of female T cells under low O₂ because percentage of apoptotic cells was similar at both O₂ concentrations.