Immunopathphysiology of human leptospirosis : study of innate immune response ; Immunopathologie de la leptospirose humaine : exploration de la réponse immunitaire innée.

Leptospirosis is a bacterial zoonosis caused by Leptospira and affecting 1 million people each year worldwide and mainly in tropical areas such as Reunion Island. Usual presentations encompass flu-like syndrome to multiorgan failure with mortality rate between 5 to 10%. To date, pathophysiology in humans is poorly understood, notably the capacity of innateimmunity to mount a robust response to clear pathogen or to induce tissue damages and contributing to disease severity. Our study aimed at assessing the role of innate immune cells and molecules within the first days of leptospiral infection.Using blood samples, we performed quantitative and qualitative assessment of circulating innate immune cells from leptospirosis cases and healthy controls. The first study explored the levels of gamma-delta T-cells (γδT-cells), a subset of unconventional T cells with innate immune functions. Gamma-delta T cells were found deeply decreased and levels wereinversely correlated to bacterial burden and liver damage. The second study focused on membrane bound receptors indicative of activation and tissue migration ability of neutrophil polymorphonuclear cells: CD15, CD11b, and CD182. Although neutrophil rates were high in leptospirosis cases, the levels of studied receptors were either lower (CD15) or identical to healthy controls (CD11b, CD182). In addition, only low levels of interleukin-8, a key chemokine for neutrophils, was detected in patients. Lastly, we ascertained the plasmatic levels of several shed cell adhesion molecules notably expressed by endothelial cells. The levels of soluble E-selectin and ICAM-1 were significantly increased compared to controls, while P-selectin level was lower. We did not find any correlation with disease severity or organ failure. This finding indicates that endothelial cell may be activated but further experiments are warranted to explain the functional impact of our findings. Altogether, our results add to the field of knowledge of leptospirosis pathophysiology, and in particular the ...