Levels of cysteinyl leukotriene receptor mRNA in human peripheral leucocytes: significantly higher expression of cysteinyl leukotriene receptor 2 mRNA in eosinophils.

Abstract

Cysteinyl leukotrienes (CysLTs) have been implicated as important contributors in the pathophysiology of asthma and their biological effects are mediated by at least two distinct G-protein-coupled receptors. cDNA sequences of cysteinyl leukotriene receptor 1 (CysLTR1) and cysteinyl leukotriene receptor 2 (CysLTR2) have recently been elucidated. Our aim is to explore gene expression and the comparative expression of CysLTR1 mRNA and CysLTR2 mRNA in human peripheral blood leucocytes. Gene expression of CysLTR1 and CysLTR2 mRNAs in human peripheral blood eosinophils, neutrophils, monocytes and T lymphocytes has been measured by competitive reverse transcription-polymerase chain reactions using RNA or DNA competitors. (a) When cellular levels of CysLTR1 mRNA were normalized to those of G3PDH mRNA, the relative concentration of CysLTR1 mRNA in eosinophils (43.8 +/- 37.2, n = 29) was significantly higher than that in neutrophils (18.7 +/- 23.3, n = 11), monocytes (0.93 +/- 1.1, n = 10) and T lymphocytes (3.4 +/- 2.4, n = 11). (b) When measured using each DNA competitor, mRNAs for both types of CysLTR coexisted in each type of leucocyte. The ratio of CysLTR1 mRNA to CysLTR2 mRNA was significantly lower in eosinophils (0.65 +/- 0.42, n = 12) than in neutrophils (6.9 +/- 4.9, n = 12), monocytes (1.8 +/- 0.9, n = 10) and T lymphocytes (4.5 +/- 5.7, n = 10). (c) Human umbilical vein endothelial cells expressed CysLTR2 mRNA, but not CysLTR1 mRNA. These studies reveal that CysLTR1 mRNA and, in particular, CysLTR2 mRNA are abundantly expressed at high levels in eosinophils, raising the possibility that CysLTR2 may have an important physiological role in eosinophils and a CysLTR2 antagonist may be a good target for preventing signal transduction by CysLTs in eosinophils.