Crosstalk between platelets, B. abortus and immune cells

Abstract

Brucellosis is an infectious disease elicited by bacteria of thegenus Brucella. Platelets have been extensively described asmediators of hemostasis and responsible for maintaining vascularintegrity. Nevertheless, they have recently got involved inthe modulation of innate and adaptive immune responses. Wehave already demonstrated a crosstalk between B. abortus andmonocytes. However, the role of platelets during monocyte/macrophageinfection by these bacteria remains unknown. The aim ofthis study was to investigate whether platelets are involved in thedevelopment of Brucella-mediated infection. To start evaluatingthis, THP-1 cells (pro-monocytic human cell line) were infectedwith B. abortus-GFP (100:1) in the presence or absence of plateletsfor 4 h and the effect of platelets on the infectious capacityof Brucella was analyzed by confocal microscopy. Our resultsshowed that the presence of platelets stimulated the invasion ofmonocytes by B. abortus. Moreover, we observed that plateletsformed complexes solely with infected monocytes. Afterwards, weevaluated the ability of platelets to modulate functional aspects ofmonocytes during the infection. First, we studied the secretion ofimmunomodulatory mediators. To address this, THP-1 cells wereinfected with B. abortus in the presence or absence of plateletsfor 4 or 24 h. The supernatants from infected cells were collectedand quantified by ELISA. Next, we studied the expression ofadhesion and co-stimulatory molecules on the monocyte surfaceby flow cytometry. The presence of platelets during monocytes/macrophages infection stimulated IL-1b, IL-8 and MCP-1 secretion(p<0.01) while it inhibited the secretion of TNF-a (p<0.01). At thesame time, platelets stimulated the expression of ICAM-1 (CD54)and CD40 (p<0.01). Overall, our results indicate that plateletscan modulate the B. abortus-mediated infection of monocytesincreasing their pro-inflammatory capacity, which could promotethe resolution of the infection.