Leukotriene B₄, an activation product of mast cells, is a chemoattractant for their progenitors

Mast cells are tissue-resident cells with important functions in allergy and inflammation. Pluripotential hematopoietic stem cells in the bone marrow give rise to committed mast cell progenitors that transit via the blood to tissues throughout the body, where they mature. Knowledge is limited about the factors that release mast cell progenitors from the bone marrow or recruit them to remote tissues. Mouse femoral bone marrow cells were cultured with IL-3 for 2 wk and a range of chemotactic agents were tested on the c-kit⁺ population. Cells were remarkably refractory and no chemotaxis was induced by any chemokines tested. However, supernatants from activated mature mast cells induced pronounced chemotaxis, with the active principle identified as leukotriene (LT) B₄. Other activation products were inactive. LTB₄ was highly chemotactic for 2-wk-old cells, but not mature cells, correlating with a loss of mRNA for the LTB₄ receptor, BLT1. Immature cells also accumulated in vivo in response to intradermally injected LTB₄. Furthermore, LTB₄ was highly potent in attracting mast cell progenitors from freshly isolated bone marrow cell suspensions. Finally, LTB₄ was a potent chemoattractant for human cord blood–derived immature, but not mature, mast cells. These results suggest an autocrine role for LTB₄ in regulating tissue mast cell numbers.