Expression pattern of protease activated receptors in lymphoid cells

Highlights

• PAR₁ is the most abundant member of the PAR family present in human lymphocytes.

• Natural killer cells express PAR₁, PAR₂ and PAR₃ at mRNA and protein level.

• γδ and CD8+ T cells express PAR₁ while CD4+ T cells express mRNA for PAR₁ and PAR₂.

• B cells did not express any PAR member.

• PAR₄ was absent at mRNA level in all human lymphocyte populations.

Abstract

Protease-activated receptors (PARs) are a subfamily of four G-protein-coupled receptors mediating multiple functions. PARs expression was studied in subpopulations of human lymphocytes. Our results indicate that natural killer cells expressed mRNA for PAR₁, PAR₂ and PAR₃, CD4+ T cells expressed PAR₁ and PAR₂, while γδ and CD8+ T cells only expressed PAR₁. PAR₄ was absent at mRNA level and B cells did not express any PAR. Analyses of the cell surface PARs expression by flow cytometry were consistent with the mRNA data and also between different donors. PAR₁ is the most abundant member of the PAR family present in lymphocytes.

Introduction

Protease-activated receptors (PARs) are a unique subclass of G-protein-coupled receptors which are activated by irreversible proteolytic cleavage of the receptor, leading to the exposure of a new amino-terminus, which serves as a tethered ligand unique for each receptor [1], [2]. Three of the four members of this receptor family, PAR₁, PAR₃ and PAR₄ are cleaved and activated by thrombin and are therefore considered as functional thrombin receptors [3], [4]. In contrast, PAR₂ is activated by trypsin, Factor Xa and mast cell tryptase, but not by thrombin [2]. PARs are expressed by circulating blood cells as well as by vascular endothelial and smooth muscle cells. Human platelets express PAR₁ and PAR₄ [5], human umbilical vein endothelial cells express PAR₁, PAR₂, and PAR₃ [6], neutrophils are found to express only PAR₂ [7], eosinophils express PAR₁ and PAR₂ [8], while basophils do not express any member of the PAR receptors [9]. Furthermore, functional thrombin receptors PAR₁ but less PAR₃ have been described in human mononuclear cells [10]. Regarding lymphoid cells, it was reported that natural killer (NK) cells and a fraction of CD3/CD4+ positive cells express the thrombin receptor PAR₁ [11] and more recently, CD3+ T cells were found to express PAR₁, PAR₂ and PAR₃ and to secrete IL-6 after stimulation with PAR₁ and PAR₂ agonist peptides [12]. However, whether a distinct expression pattern of PARs in innate and adaptive lymphoid cells exist has not been fully addressed. Moreover, differential PAR₁–₄ expression in γδ T cells is unknown, although these cells play important roles in innate and adaptive immune responses. In this study, we therefore investigated the expression of PARs at the level of both mRNA and cell surface protein expression in adaptive lymphoid cells, including CD4+ T cells, CD8+ T cells, B cells and innate lymphoid cells such as NK and γδ T cells. Here, we show for the first time high expression of PAR₁ in γδ T cells.