Effects of Short Term in vitro Stress Hormone Exposure on Regulatory T Cell Number and Function in Asthma

Asthma is characterized by alterations in the immune system, including regulatory T cells (T_reg). Further alterations in T_reg numbers and/or function caused by stress hormones may be a contributing factor in asthma pathogenesis. We compared T_reg populations and the effects of Dexamethasone (DEX, a laboratory analog of cortisol) on T_reg cell number and function in patients with asthma and a control group. We isolated Peripheral Blood Mononuclear Cells (PBMC) from asthma patients (n = 7) and normal controls (n = 8) and quantified CD4⁺, CD4⁺CD25^hi and CD4⁺CD25^hiFoxP3⁺ T cells by flow cytometry. To determine the effects of in vitro stress hormones on T_reg number and function, we incubated PBMC with 10^-9 M, 10^-8 M and 10^-7 M DEX for 24 h and then CD4⁺CD25^hiFoxP3⁺ T_reg were quantified by flow cytometry. To assess function, CD4⁺CD25⁺ were separated and added to cultures of bead-stimulated CD4⁺CD25^- cells and proliferation was measured and compared to the CD4⁺CD25^- cultures incubated with beads alone. The asthma group had significantly fewer CD4⁺CD25^hi and CD4⁺CD25^hiFoxP3⁺ cells than the control group. DEX significantly decreased T_reg number in the control group but not in the asthma group. DEX had no effect on CD4⁺CD25⁺ function in either group and the suppressive capacity of the CD4⁺CD25⁺ cells was no different between the asthma group and the normal control group. These data suggest that while asthmatics have fewer T_reg than normal controls, their function does not differ. These data also suggest that T_reg from asthmatics may be less susceptible to the effects of stress hormones.