In vivo protein synthesis of circulating human T lymphocytes does not respond to a cortisol challenge within 24 h

Although immunocompetence is often measured by assessing responsiveness of lymphocytes to mitogenic stimulation in vitro, this approach may not reflect the in vivo situation. The aim of this investigation was to determine in vivo the protein synthesis rate (FSR) in isolated T lymphocytes and to study the effect of a short-term cortisol infusion on FSR.

Healthy volunteers (n=24) were randomised into 4 groups. A continuous cortisol infusion (6 microg kg(-1) min(-1)) during 6 h was given to groups 1 and 2, whereas groups 3 and 4 served as control groups and received saline infusion. Protein synthesis was studied before and after 6 h of the cortisol/saline infusion (groups 1 and 3) or 24 h after the start of the infusion (groups 2 and 4). FSR was determined in vivo by the flooding method. The isotopic enrichment of phenylalanine in plasma and lymphocyte protein was determined with gas chromatography-mass spectrometry.

The FSR in T lymphocytes was 13.6+/-0.9%/24 h as a mean value (+/-SD) of the first determination in 4 groups. There was no significant difference in FSR from the baseline value immediately after the cortisol infusion (group 1: 13.3+/-1.4%/24 h vs 13.5+/-2.8%/24 h) or 24 h after the start of the infusion (group 2: 13.6+/-0.7%/24 h vs 12.3+/-2.4%/24 h).

The metabolic activity of circulating T lymphocytes, as reflected by a quantitative measurement of in vivo protein synthesis of human T lymphocytes, was not affected by the increased level of cortisol.