The palatine tonsils are constantly exposed to ingested or inhaled antigens which, in turn, lead to a permanent activation of tonsillar immune cells, even in a basic physiological state. The aim of the present study was to investigate if the immunological activation of the human palatine tonsil is reflected by a high metabolic activity, as determined by in vivo measurement of protein synthesis. The protein synthesis rate of the tonsil was also compared with that of the circulating T-lymphocytes, the total blood mononuclear cells and the whole population of blood leucocytes. Phenotypic characterization of immune-competent cells in tonsil tissue and blood was performed by flow cytometry. Pinch tonsil biopsies were taken after induction of anaesthesia in healthy adult patients ( n =12) scheduled for ear surgery, uvulopalatopharyngoplasty or nose surgery. Protein synthesis was quantitatively determined during a 90-min period by a flooding-dose technique. The in vivo protein synthesis rate in the palatine tonsils was 22.8±5.7%/24 h (mean±S.D.), whereas protein synthesis in the circulating T-lymphocytes was 10.7±3.4%/24 h, in mononuclear cells was 10.8±2.8%/24 h and in leucocytes was 3.2±1.2%/24 h. CD3 + lymphocytes were the most abundant cell population in the tonsil. The in vivo protein synthesis rate in human tonsils was higher compared with the circulating immune cells. This high metabolic rate may reflect the permanent immunological activity present in human tonsils, although cell phenotypes and activity markers do not explain the differences.

In order to investigate the immediate (i.e. within 3h) response of albumin synthesis to the administration of endotoxin, as a model of a moderate and well controlled catabolic insult, two measurements employing L -[ 2 H 5 ]phenylalanine were performed in 16 volunteers. One group ( n = 8) received an intravenous injection of endotoxin (4ng/kg; lot EC-6) immediately after the first measurement of albumin synthesis, whereas the other group received saline. A second measurement was initiated 1h later. In the endotoxin group, the fractional synthesis rate of albumin was 6.9±0.6%/day (mean±S.D.) in the first measurement. In the second measurement, a significant increase was observed (9.6±1.2%/day; P <0.001). The corresponding values in the control group were were 6.6±0.6%/day and 7.0±0.6%/day respectively (not significant compared with first measurement and P <0.001 compared with the second measurement in the endotoxin group). The absolute synthesis rates of albumin were 148±35 and 201±49mg·kg -1 ·day -1 before and after endotoxin ( P <0.01). In the control group, the corresponding values were 131±21 and 132±20mg·kg -1 ·day -1 (not significant compared with the first measurement and P <0.01 compared with the second measurement in the endotoxin group). In conclusion, these results indicate that albumin synthesis increases in the very early phase after a catabolic insult, as represented by the administration of endotoxin.