Cysteinyl-leukotriene type 1 receptors transduce a critical signal for the up-regulation of eosinophilopoiesis by interleukin-13 and eotaxin in murine bone marrow

Novel role of eotaxin and IL‐13 in regulating bone‐marrow eosinophilopoiesis, and a critical role for CysLT1R receptors in transducing eotaxin/IL‐13 signals. IL‐13 and eotaxin play important, inter‐related roles in asthma models. In the lungs, CysLT, produced by the 5‐LO‐LTC4S pathway, mediate some local responses to IL‐13 and eotaxin; in bone marrow, CysLT enhance IL‐5‐dependent eosinophil differentiation. We examined the effects of IL‐13 and eotaxin on eosinophil differentiation. Semi‐solid or liquid cultures were established from murine bone marrow with GM‐CSF or IL‐5, respectively, and the effects of IL‐13, eotaxin, or CysLT on eosinophil colony formation and on eosinophil differentiation in liquid culture were evaluated, in the absence or presence of: a) the 5‐LO inhibitor zileuton, the FLAP inhibitor MK886, or the CysLT1R antagonists, montelukast and MK571; b) mutations that inactivate 5‐LO, LTC4S, or CysLT1R; and c) neutralizing mAb against eotaxin and its CCR3 receptor. Both cytokines enhanced GM‐CSF‐dependent eosinophil colony formation and IL‐5‐stimulated eosinophil differentiation. Although IL‐13 did not induce eotaxin production, its effects were abolished by anti‐eotaxin and anti‐CCR3 antibodies, suggesting up‐regulation by IL‐13 of responses to endogenous eotaxin. Anti‐CCR3 blocked eotaxin completely. The effects of both cytokines were prevented by zileuton, MK886, montelukast, and MK571, as well as by inactivation of the genes coding for 5‐LO, LTC4S, and CysLT1R. In the absence of either cytokine, these treatments or mutations had no effect. These findings provide evidence for: a) a novel role of eotaxin and IL‐13 in regulating eosinophilopoiesis; and b) a role for CysLTRs in bone marrow cells in transducing cytokine regulatory signals.