Decreased HLA-DR antigen-associated invariant chain (CD74) mRNA expression predicts mortality after septic shock

Abstract

Introduction: Septic syndromes remain the leading cause of mortality in intensive care units (ICU). Septic patients rapidly develop immune dysfunctions, the intensity and duration of which have been linked with deleterious outcomes. Decreased mRNA expressions of major histocompatibility complex (MHC) class II-related genes have been reported after sepsis. We investigated whether their mRNA levels in whole blood could predict mortality in septic shock patients.

Methods: A total of 93 septic shock patients were included. On the third day after shock, the mRNA expressions of five MHC class II-related genes (CD74, HLA-DRA, HLA-DMB, HLA-DMA, CIITA) were measured by qRT-PCR and monocyte human leukocyte antigen-DR (mHLA-DR) by flow cytometry.

Results: A significant correlation was found among MHC class II related gene expressions. Among mRNA markers, the best prognostic value was obtained for CD74 (HLA-DR antigen-associated invariant chain). For this parameter, the area under the receiver operating characteristic curve (AUC) was calculated (AUC = 0.67, 95% confidence interval (CI) = 0.55 to 0.79; P = 0.01) as well as the optimal cut-off value. After stratification based on this threshold, survival curves showed that a decreased CD74 mRNA level was associated with increased mortality after septic shock (Log rank test, P = 0.0043, Hazard Ratio = 3.0, 95% CI: 1.4 to 6.5). Importantly, this association remained significant after multivariate logistic regression analysis including usual clinical confounders (that is, severity scores, P = 0.026, Odds Ratio = 3.4, 95% CI: 1.2 to 9.8).

Conclusion: Decreased CD74 mRNA expression significantly predicts 28-day mortality after septic shock. After validation in a larger multicentric study, this biomarker could become a robust predictor of death in septic patients.

Figures

Figure 1

MHC class II related genes and protein expressions in survivors and non-survivors after septic shock. Circulating monocyte HLA-DR expression mHLA-DR – number of antibodies bound per cell (AB/C) was measured by flow cytometry and major histocompatibility class II related genes mRNA levels were evaluated by qRT-PCR in blood samples obtained from 93 septic shock patients at Day 3 or Day 4 after the onset of shock. Results are presented as box-plots as well as individual values in survivors (n = 66) and non-survivors (n = 27). Mann Whitney U-test was used to compare results between groups. CD74, HLA-DR antigen-associated invariant chain, CIITA, class II transactivator; HLA-DR/DM, human leukocyte antigen-DR/DM.

Figure 2

Prognostic value of mHLA-DR and CD74 mRNA levels in septic shock patients.CD74 mRNA level and circulating monocyte HLA-DR expression (mHLA-DR) were measured in blood samples obtained from 93 septic shock patients at Day 3 or Day 4 after the onset of shock. A). Receiver operating characteristic curves were established for these two parameters. The area under the curve was 0.67 for CD74 (95% confidence interval (95% CI): 0.55 to 0.79; P = 0.01) and 0.70 (95% CI: 0.57 to 0.83; P = 0.003) for mHLA-DR. B). Kaplan-Meier survival curves were established after stratification based on CD74 mRNA level cut-off value (= 0.185, optimized Youden index). A significant difference was measured between the two curves (Log rank test, P = 0.0043; Hazard Ratio = 3.0, 95% CI: 1.4 to 6.5). C). Similar analysis was performed for mHLA-DR. Cut-off value = 1,662 AB/C. Log rank test: P <0.0001, Hazard Ratio = 5.8, 95% CI = 2.6 to 12.9.

Figure 3

Major histocompatibility class II related molecules and antigen presentation process. The MHC class II network was generated through the use of IPA (Ingenuity® Systems, http://www.ingenuity.com).