Background: Reportedly G-CSF can accelerate granulocyte maturation (Lord et al. 1991). However, we have evidence from an in vivo culture system (diffusion-chambers), where cells cannot escape, that G-CSF does not accelerate the maturation rate (Wang et al. 1999). We now wanted to measure granulocyte maturation directly in vivo.

Methods: Mouse granulocyte precursors were labeled with BrdU in vivo (a marker of DNA synthesis) before injecting a long-acting G-CSF (SD/01). With flow cytometry and relevant antibodies we measured incorporation of BrdU in DNA and the expression of the granulocyte maturation antigen Gr1. In this way we could investigate cell fluxes from the proliferative to the non-proliferative granulocyte compartments in bone marrow, and from bone marrow to blood.

Results: SD/01 mobilized granulocytes from bone marrow to blood, markedly increasing their concentration here for several days. Newly produced granulocytes (Gr1⁺ BrdU⁺) traveled faster to blood in the test mice, but their Gr1 expression was lower than in controls. According to this criterion marrow cells of the granulocyte lineage were also less mature than control cells after the SD/01 treatment. Cell density separation of the bone marrow cells, combined with flow cytometry showed that SD/01 skewed the granulopoiesis towards lower cell densities, indicating a less mature phenotype, with cells expressing less Gr1.

Conclusion: Our data support the hypothesis that G-CSF does not accelerate granulocyte maturation.

REFERENCES

Lord, B.I., Molineux, G., Pojda, Z., Souza, L.M., Mermod, J.J. & Dexter, T.M. 1991. Blood 77, 2154-59.

Wang, X.L., Fjerdingstad, H., Strøm-Gundersen, I.& Benestad, H.B. Stem Cells 17, 253-64.