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

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... normal controls (n = 8) and quantified CD4 + , CD4 + CD25 hi and CD4 + CD25 hi FoxP3 + 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 hi FoxP3 + T reg were quantified by flow cytometry. To assess function, CD4 + CD25 + were separated and added to cultures of bead-stimulated CD4 + CD25cells and proliferation was measured and compared to the CD4 + CD25cultures incubated with beads alone. The asthma group had significantly fewer CD4 + CD25 hi and CD4 + CD25 hi FoxP3 + 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.