The TNF-α release increased slightly by glutamine concentrations of 300 and 600 μm. In comparison with glutamine concentrations of 250 and 2000 μm, our study shows no significant differences of IL-2 and TNF-α release (Tables 2 and 4). These results are consistent with the studies already presented by Yaqoob et Calder [11] and Rohde et al. [1]. In Z-VAD-FMK supplier the study by Yaqoob et Calder, maximum levels of IL-2

and TNF-α release are achieved at a glutamine concentration of 100 μm, which do not increase at higher glutamine levels any more. This threshold value is not confirmed by our study. In our study, we could show that the cytokine production is not impaired at a glutamine concentration which correlates to the half of the physiological GSK-3 beta phosphorylation concentration. Only at a glutamine concentration below 100 μm, the IL-2 and TNF-α release could be compromised. In the study by Rohde et al., who worked at concentrations of 300 μM and 600 μM are maximum values of IL-2 and TNF-α release already reached at 300 μM glutamine supplemention. This is similar to our findings in

this study even though we did not cover a threshold of 100 μm. It would be interesting to create study designs with gradations between the entirely absence of glutamine and a concentration of 100 μm glutamine in the culture medium. This could lead to a definition of a threshold level of glutamine for an increase in the cytokine production or it could show a decrease in cytokine production by the absence of glutamine. In contrast to Yacoob et Calder and Rohde et al., we used different GNAT2 stimulants and different durations of incubations for the activation of lymphocytes in vitro. Perhaps, this difference might have influenced the comparability to our study. The fact, that glutamine in general, increases the cytokine production of IL-2 and TNF-α, cannot be confirmed by our study. We showed that there is no significant difference in the cytokine production between glutamine concentrations of 250 and 2000 μm, from which we conclude

that a glutamine concentration which affects the cytokine production must be lower than 250 μm. The decreased IL-2 and TNF-α release in the tertiles with high expressors on average by 17% and 11% are calculated from the mean values seen in Tables 2 and 4. The results are not significant (P = 0,128 and P = 0,104) but should be rated as a tendency. The transfer of our conclusions to a clinical scenario is difficult. The fact that a decreasing glutamine concentration has clinical relevance and that it weakens the immune system remains undisputable [31]. Also that a glutamine supplementation under immunonutrition reduces the mortality in certain groups of patients has already been demonstrated [32, 33]. Many clinical studies have revealed that the glutamine concentration decreases in stressful situations, such as severe burns or sepsis, but it remains over a concentration of 300 μm [4–6, 34].