Ligand‐activated natural killer T lymphocytes promptly produce IL‐3 and GM‐CSF in vivo: relevance to peripheral myeloid recruitment

Natural killer (NK) T cells are prominent for their prompt IL‐4 and IFN‐γ production upon TCR ligation that enables them to influence acquired immune responses. In the present study we provide evidence that the regulatory functions of this particular T cell subset extend to the myeloid compartment of bone marrow and spleen through its production of hematopoietic growth factors. Bone marrow and spleen NKT cells responded to a single injection of their specific ligand α‐galactosylceramide (α‐GalCer) by producing both IL‐3 and granulocyte‐macrophage colony stimulating factor (GM‐CSF), whose colony‐stimulating activity became detectable in the serum as early as 1 h post treatment. These cytokines were not produced in mice lacking NKT cells (CD1d–/–), whose exclusive involvement in this biological activity was further confirmed by intracellular immuno‐staining. Growth factor production was accompanied by significant changes in the myeloid compartment of treated mice, namely mobilization of myeloid progenitors (colony‐forming unit cells, CFU‐C) and neutrophils from the bone marrow to the periphery. Taken together, our data support the notion that activated NKT cells influence innate immune responses by recruiting myeloid progenitors and granulocytes to the periphery through their production of hematopoietic growth factors.