The chemokine receptor CXCR4 is expressed within the mast cell lineage and its ligand stromal cell-derived factor-1alpha acts as a mast cell chemotaxin.

In this study we provide evidence that the chemokine stromal cell-derived factor-1alpha (SDF-1alpha) acts as a mast cell chemoattractant through interactions with its receptor CXCR4 expressed on mast cell progenitors in the blood as well as on in vitro-developed and leukemic mast cells. We found expression of CXCR4 on cord blood-derived mast cells (CBMC) and on the human mast cell line HMC-1, analyzed by RNAse protection assay and flow cytometry. SDF-1alpha induced intracellular calcium mobilization in HMC-1 cells and was chemotactic for both HMC-1 cells and CBMC. The activity of SDF-1alpha was completely blocked by treating the cells with pertussis toxin, indicating the involvement of Gi-proteins in the signaling. By applying a transwell assay we could show that SDF-1alpha induces migration of a cell population in peripheral blood that is enriched for cells with the capacity to differentiate into mast cells. These findings thus suggest a mechanism by which human mast cell progenitors may be recruited from circulation into the tissue.

The potential of human mast cell progenitors to differentiate into mature mast cells remains after prolonged culture with flt3 ligand, interleukin-3 or granulocyte-macrophage colony stimulating factor.

Stem cell factor (SCF) plays a key role in the development of mast cells from haemopoietic progenitor cells. In this study we have investigated the effect of the early acting haemopoietic cytokines flt3 ligand (FL), IL-3 and GM-CSF on the SCF-dependent differentiation of mast cells from cord blood mononuclear cells. By using delayed addition of SCF, we examined the potential of mast cell progenitors to keep their capacity to differentiate into mast cells after exposure to factors signalling differentiation into other lineages. Culture with either cytokine for 3 weeks before transfer to SCF-containing medium resulted in the development of mast cells in all cultures. The appearance of mast cells was attenuated when the cells had been in culture with IL-3 or GM-CSF prior to culture in SCF, compared to cultures exposed to SCF alone for 7 weeks. However, a proportion of the cells had not lost the capacity to develop into mast cells. In contrast, in cultures initiated with FL and transferred to medium containing SCF, the same amount of mast cells developed as in the SCF cultures. Thus, cells committed to the mast cell lineage appear to be resistant to the lineage directives of IL-3 and GM-CSF and keep their potential to differentiate into mature mast cells.

Demonstration of mast-cell chemotactic activity in nasal lavage fluid: characterization of one chemotaxin as c-kit ligand, stem cell factor.

Mast cells are known to accumulate in tissue during allergic inflammation. However, the chemotaxins responsible are undefined. Using a modified Boyden chamber and the human mast-cell line HMC-1, we first identified mast-cell chemotactic activity in nasal lavage fluid collected before the pollen season after allergen provocation of allergic patients (n=29) (mean migratory response compared to medium control was 121%, range 85-198%). Mast-cell chemotactic activity was also detected in lavage fluid collected after allergen provocation at the end of a Swedish birch-pollen season from three different treatment groups: topical steroid treatment with budesonide; the topical antihistamine, levocabastine; and placebo. There was no significant difference in mast-cell chemotactic activity between nasal lavage fluid collected from the placebo group (mean=102%), the budesonide-treated group (mean=114%), or the levocabastine group (mean=125%). Stem cell factor (SCF), a known mast-cell chemotaxin, was present in the nasal lavage fluids from all three groups, and correlated with the mast-cell chemotactic activity (r=0.67, P<0.01). The mast-cell chemotactic activity was inhibited (range 5-100%) in some, but not all, nasal lavage fluids by a polyclonal antibody directed against SCF. This report describes the presence of mast-cell chemotactic activity in nasal lavage fluid during an allergic reaction. These findings show that SCF may play a pivotal role in the recruitment of mast cells in allergic rhinitis.

Stem cell factor, but not flt3 ligand, induces differentiation and activation of human mast cells.

We have examined the effect of human ligand for the flt3/flk2 tyrosine kinase receptor on the differentiation of human mast cells in suspension cultures. We also explored the effect of flt3 ligand (FL) on the human mast cell line HMC-1 and mRNA expression of flt3/flk2 on in vitro developed human mast cells and HMC-1. The growth of cord blood mononuclear cells in suspension cultures was increased when cells were cultured in the presence of FL compared with cells cultured in the presence of stem cell factor (SCF). When SCF and FL were combined, the total cell growth was increased further. Our data show that Fl by itself neither induced differentiation of mast cells nor acted in the SCF-dependent differentiation of human cord blood-derived mast cells (CBMC). Furthermore, no effects of FL were found on the proliferation of HMC-1 cells or the induction of early-immediate response genes in HMC-1 cells. In addition, neither HMC-1 cells nor CBMC expressed mRNA for flt3. As has been shown before, SCF and FL have little biological effect on their own but synergize well with a number of other hematopoietic growth factors. This study shows that a major difference between FL and SCF is that only SCF affects the differentiation and activation of mast cells.