Mononuclear phagocytes are central elements in host defense against a variety of invading microorganisms and in the pathogenesis of sepsis. They play a central role in the immune response by presenting microbial antigens to T lymphocytes and producing cytokines, thus initiating and regulating both cellular and humoral immune responses. HLA-DR expression plays a central role in the processing of antigen by macrophages and helper T cells. Several previous studies demonstrated that low HLA-DR expression on monocytes was found in patients with sepsis (13
), trauma (9
), and severe burns (26
). Our study extends those observations and demonstrates significantly lower monocyte HLA-DR expression in all patients with severe sepsis compared to healthy controls. We also revealed that septic patients who survived had significantly higher levels of HLA-DR expression compared to nonsurvivors during a 17-day follow-up. This was found at almost all time points (except day 10), which means that HLA-DR expression may serve as a dynamic prognostic marker not only on admission but also during the whole septic episode in patients with severe infections.
On the other hand, during inflammatory syndromes, a number of proinflammatory molecules are released and serve as modulators of the immune response. Several studies have already been published that show increased concentrations of various cytokines in the serum of patients with sepsis, emphasizing their possible contribution to predicting the final outcome in these patients (5
). Elevated levels of TNF-α and IL-6 have been associated with increased mortality from sepsis (16
), and some investigators have indicated that IL-6 levels are a good prognostic parameter in the early phase of sepsis. However, sepsis is associated not only with the exacerbation of the production of proinflammatory cytokines but also with the release of many anti-inflammatory cytokines, such as IL-10 and TGF-β1. Previous investigations have indicated that TGF-β1 represses the production of inflammatory cytokines by activated macrophages and induces the release of soluble TNF receptor and IL-1 receptor α. It has been shown that mean plasma TGF-β1 levels were increased in patients with sepsis syndrome compared to healthy donors (19
). Except for TGF-β1, IL-10 is one of the immunosuppressive mediators postulated to play an important role in down-regulation of the immune response. Elevated levels of IL-10 have been associated with increased mortality from septic shock (27
Our data indicated that all cytokine levels measured were significantly higher in septic patients than healthy individuals, as expected. Monitoring the serum cytokine levels was a good marker of the immune status and outcome, but at different time intervals, because TNF-α levels were significantly higher in nonsurvivors on days 13 and 17, IL-6 was higher only on day 3, and IL-10 was higher on days 3, 10, and 13. These findings are in accordance with previous studies of ours (12
) and other investigators (33
), who noted that TNF-α and IL-10 had a significant prognostic value for the final outcome.
On the contrary, HLA-DR expression on monocytes was significantly higher in survivors both at admission and at almost all time intervals. Therefore, according to our findings, monocyte HLA-DR expression seems to be an early and constant predictive marker for the prognosis of outcome in severe sepsis, while the main pro- and anti-inflammatory cytokine levels were significantly higher in a rather later stage. There seems to be a relationship between HLA-DR expression and cytokine synthesis, because we detected an inverse correlation between monocyte HLA-DR expression and IL-10 and IL-8 concentrations, as well as with the IL-10/TNF-α ratio. Interestingly, we detected that serum IL-10 levels on day 3 inversely affected monocyte HLA-DR expression on day 10 (P
< 0.05). Similar findings have been reported by other investigators, who demonstrated that IL-10 induces in vitro the downregulation of HLA-DR surface expression of “normal” monocytes and of immature dendritic cells obtained from peripheral mononuclear cells, with accumulation of MHC II molecules in intracellular compartments (11
Concerning TGF-β1, we found significantly higher levels of TGF-β1 in survivors with severe sepsis compared to nonsurvivors on admission. These results might be interpreted in terms of the beneficial effect of TGF-β1 on the hemodynamic compromise of septic shock in a previous murine model (23
). In that study, it was shown that TGF-β1 inhibited inducible nitric oxide synthetase mRNA and NO production in vivo in vascular muscle cells, after its induction by cytokines critical in the sepsis cascade. TGF-β1 was shown in vitro to inhibit IFN-γ-induced HLA-DR surface expression of various cell types through a transcriptional effect (7
). TGF-β1 has also been described as downmodulating the monocyte surface expression of HLA-DR in association with IL-10 (10
). In the present study, we found a significant inverse correlation between monocyte HLA-DR expression and TGF-β1 concentrations on days 10 and 17, which is in accordance with the previous observations.
On a clinical basis, it is noteworthy that there was no difference in the prevalence of bacteremia and gram-negative infection between survivors and nonsurvivors, while the frequencies of organ dysfunction were similar in both groups.
In conclusion, analysis of our data indicates that dynamic monitoring of the immune status of septic patients may contribute to the estimation of the death risk in relation to other clinical or laboratory markers. Pro- versus anti-inflammatory response may be sequentially identified at different time points by measuring certain serum cytokine levels in correlation with peripheral blood monocyte HLA-DR expression. The presence of immunoparalysis seems to be the main risk factor of poor outcome in patients with severe sepsis, as indicated by the diminished HLA-DR expression and the increased serum IL-10 levels. Monocyte HLA-DR expression seems to be an early prognostic marker for survival, while serum IL-10 levels may be a good marker for identification of patients with a guarded prognosis in a rather later stage.