TREM-1 Expression on the Surface of Neutrophils in Patients With Visceral Leishmaniasis Is Associated With Immunopathogenesis

Abstract

Visceral leishmaniasis (VL) is a systemic chronic and potentially fatal disease for humans. Mechanisms related to the dysregulation of the inflammatory response may be involved in both the pathogenesis and prognosis of VL. Triggering Receptor Expressed on Myeloid Cells-1 (TREM-1) is a receptor constitutively expressed on neutrophils and monocyte subsets. The protein serves to regulate and amplify inflammatory responses. This study aimed to evaluate the expression profile of TREM-1 on the surface of neutrophils from patients with VL at varying time points during leishmanicidal treatment. For this purpose, neutrophils were isolated from the peripheral blood of patients with VL at different stages of treatment, which include 0, 7, and 30 days after treatment. Surface TREM-1 expression was assessed by immunophenotyping neutrophil populations. In addition, the association of TREM-1 expression on the surface of neutrophils with clinical and laboratory parameters and serum levels of inflammatory mediators was also evaluated. Results demonstrate a lower surface expression of TREM-1 in VL patients in the absence of treatment. However, increased levels of TREM-1 expression were observed 7 and 30 days after the start of treatment, with levels similar to those of healthy controls. TREM-1 expression was directly correlated with lymphocyte and erythrocyte count and indirectly correlated with spleen and liver size. Furthermore, elevated levels of TREM-1 expression were also correlated with lower serum levels of interleukin (IL)-22. Taken together, these results suggest that infection by Leishmania infantum leads to depressed TREM-1 expression on the neutrophil surface and may contribute to the inflammatory imbalance that characterizes active VL disease.

Keywords: Leishmania infantum; TREM-1; inflammation; neutrophils; visceral leishmaniasis (VL).

Figure 1

Expression of surface TREM-1 in neutrophils from visceral leishmaniasis (VL) patients at different times of leishmanicidal treatment and healthy controls (HCs). Neutrophils from patients with VL (n = 8) and healthy donors (n = 8) were isolated from the peripheral blood, and (A) the frequency and (B) MFI of neutrophils expressing TREM-1 were assessed by flow cytometry. Bars represent the mean ± SEM. Mann–Whitney test or Student’s t test were used to compare patients’ treatment times (VL D0, VL D7, and VL 30) with the HC, and the Friedman test with Dunn’s posttest or one-way ANOVA were used for paired analysis of patients in treatment times (VL D0, VL D7, and VL D30). *p < 0.05; **p < 0.01. (C) Cluster analysis and heatmap expressing the frequency and MFI of TREM-1 in the neutrophils of patients with VL at different times of treatment and in HCs. Fold changes were calculated, and statistically significant differences are highlighted in blue and red.

Figure 2

Correlation between MFI of TREM-1 and (A) neutrophil frequency, (B) MFI CD11b, and (C–G) laboratory parameters and clinical and IL-22 serum levels from patients with VL at different times of leishmanicidal treatment. Spearman correlation test. Patients with VL before treatment are represent in red; and after treatment initiation with 7 days in blue, and 30 days in green.

Figure 3

(A) Correlation between sTREM-1 with TNF-a serum levels from patients with VL at different times of leishmanicidal treatment. Spearman correlation test. (B) Cluster analysis and heatmap expressing serum inflammatory mediators in VL patients at different times of leishmanicidal treatment. Fold changes have been calculated, and significant differences are highlighted in blue.