Identification of immunological biomarkers of macrophages related to specific compartmentalization of in lung and liver in mouse model of septic shock

Introduction

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. The complex pathophysiology of sepsis is associated with pro- and anti-inflammatory response, a pro-coagulant state, endothelial dysfunction and tissue hypoxia. These mechanisms lead to progressive multi organ failure. Although this is a systemic process, the pathophysiological of sepsis differs from organ to organ, and from organ to peripheral blood. Our hypothesis to explain this compartmentalization of responses is a distinct population of resident tissue macrophages, as well as a distinct migration of monocytes in target organ. Indeed, the macrophages and monocytes can start the clinical syndrome of sepsis via transcription of genes involved in inflammation. Moreover, macrophages can induce endothelial injury by release reactive oxygen species. Also hypoxia decreases expression of M1 polarization markers and increases the M2 marker. Identification of biomarkers related to specific organs (beyond the blood) will improve the understanding specific organ failure. In this way, the aim of this study was compared to the systemic inflammatory response with the lung and the liver, two organs most affected during sepsis as well as understanding the role of macrophages in this compartmentalization. For this, a murine polymicrobial sepsis model induced by caecal ligation and puncture (CLP) was used.

Methods

Moderate sepsis was induced by the CLP in C57BL/6 male mice (n = 63), divided into 4 groups: Basal, Sham 1 day and 5 days, CLP 1 days and 5 days. Then, we analyzed histological changes, cytokine profile (by ELISA and PCR), oxidative imbalance (expression of SOD, CAT and iNOS) and polarization markers (CD₈₆and CD₂₀₆) by immunohistochemistry.

Results

Respiratory and liver failure was confirmed by histology and also by a decrease of pressure oxygen in arterial blood (PaO₂) and increase of bilirubin level after 5 days of CLP. Moreover CLP induced a plasma increase in the level of TNFα, IL-6, IL-10, KC and CCL2 in the first 24 hours after CLP, but with a progressive decrease at 5 days. On the other hand, our original results show that the level of some of the cytokines in the liver and the lung differ from the systemic level during sepsis. Indeed, there are increase in CCL2 and its receptor CCR2 in the lung compared to the liver, whereas in the liver rather a decrease in the expression of CX3CL1/CX3CR1, that is not altered in the lung. We were also able to highlight a more marked oxidative imbalance in the liver than in the lung. Also, we observed that CLP increases the expression of M1 CD₈₆ and M2 CD₂₀₆ markers in the liver and lung at 5 days, but with a total number of CD₈₆-labeled cells, three times greater in the liver.

Conclusion

These results support the hypothesis of a compartmentalization of the inflammatory response in sepsis, characterized by an early inflammatory response in the lung, and later chronic phase in the liver. The lung cells maybe are more resistant to having their immune functions turned off. In contrast, the liver will be more sensitive to deactivations. This compartmentalization involved the migration of monocytes: CCL2/CCR2 and CX3CL1/CX3CR1 associate with the oxidative stress.