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Introduction Although major changes of the immune system have been described in sepsis, it has never been studied whether these may differ in relation to the type of underlying infection or not. This was studied for the first time. Methods The statuses of the innate and adaptive immune systems were prospectively compared in 505 patients. Whole blood was sampled within less than 24 hours of advent of sepsis; white blood cells were stained with monoclonal antibodies and analyzed though a flow cytometer. Results Expression of HLA-DR was significantly decreased among patients with severe sepsis/shock due to acute pyelonephritis and intraabdominal infections compared with sepsis. The rate of apoptosis of natural killer (NK) cells differed significantly among patients with severe sepsis/shock due to ventilator-associated pneumonia (VAP) and hospital-acquired pneumonia (HAP) compared with sepsis. The rate of apoptosis of NKT cells differed significantly among patients with severe sepsis/shock due to acute pyelonephritis, primary bacteremia and VAP/HAP compared with sepsis. Regarding adaptive immunity, absolute counts of CD4-lymphocytes were significantly decreased among patients with severe sepsis/shock due to community-acquired pneumonia (CAP) and intraabdominal infections compared with sepsis. Absolute counts of B-lymphocytes were significantly decreased among patients with severe sepsis/shock due to CAP compared with sepsis. Conclusions Major differences of the early statuses of the innate and adaptive immune systems exist between sepsis and severe sepsis/shock in relation to the underlying type of infection. These results may have a major impact on therapeutics.

Dear Editor: Reintam et al. [1] discuss intra-abdominal hypertension (IAH) as an independent risk factor of mortality in a presumed risk population of critically ill patients. The authors use univariable logistic regression to identify risk factors for ICU mortality followed by multiple logistic regression to identify risk factors that are independently associated with ICU mortality. In a stepwise multiple regression analysis ([1, Table 3)], it is shown that APACHE II score at admission in the ICU was a strong independent predictor of ICU mortality. IAH during the ICU period and lactate at admission displayed only borderline association with ICU mortality (p values 0.033 and 0.034 for IAH and lactate, respectively). Consequently, areas under curves (AUCs) in receiver operating characteristic (ROC) analysis were good for APACHE II score (0.876), fair for lactate (0.771), and poor for intra-abdominal pressure (0.530) [2]. This suggests that intraabdominal pressure alone has very low predictive ability for ICU mortality, no better than tossing a coin [2]. A more informative approach would be to assess the predictive ability of the multiple regression model for ICU mortality. First, it should be ascertained with one of the goodness-of-fit tests (e.g., HosmerLemeshow test) that fitting of the model does not present serious problems. Then, a ROC curve, which is a plot of sensitivity as a function of 1-specificity, for the possible cutoffs of predicted probability by the model in regard to the binary outcome (ICU 28-day or 90-day death or survival), should be created [3]. The ROC curve of the full model would be rather more informative than ROC curves of single variables, because it summarizes predictive power for all possible values of ICU death probability, as predicted by the full model. The above approach would more precisely estimate the predictive ability of intra-abdominal pressure for ICU mortality, adjusting for the other two independent predictors (APACHE II score and lactate).