Neutropenia induces expansion of myeloid hematopoietic progenitors and myelopoietic cytokines. (A) H&E-stained femora of neutropenic and control C57BL/6 mice on day 8 of treatment with granulocyte/erythrocyte ratio (microscope: Apotome, Zeiss; acquisition software: Axiovision Rel 4.8.2, Zeiss; magnification 63× and 20×). Note that marrow cellularity remains high in neutropenic animals and the increased granulocyte/erythrocyte ratio in antibody-treated mice. (B) Marrow flow cytometry including gating strategy in C57BL/6 wild-type mice. Myeloid progenitor cells (lin⁻ CD127⁻ Sca-1⁻ c-kit⁺) were further differentiated into GMP (CD16/32⁺ CD34⁺), CMP (CD16/32⁻ CD34⁺), and MEP (CD16/32⁻ CD34⁻). Note expansion of the LSK population and increase of GMP at the cost of MEP. (C) Absolute marrow cell numbers calculated to reflect total cell counts in both hind limbs (n = 3). RB6-8C5: p(LSK) < 0.001; p(GMP) = 0.003; p(MEP) = 0.02; p(CMP) = not significant (NS); 1A8: p(LSK) = 0.01; p(GMP) = 0.03; p(MEP) = NS; p(CMP) = NS. (D) Plasma G-CSF and M-CSF levels in control and neutropenic C57BL/6 mice. Note the significant increase of G-CSF (n = 3). G-CSF: p(RB6-8C5) = 0.002; p(1A8) < 0.001; M-CSF: p(1A8 and RB6-8C5) = NS. (E) Plasma IL-17 and IL-23 levels in control and neutropenic C57BL/6 mice (n = 3 each group). IL-17: p(RB6-8C5) = 0.05; p(1A8) = 0.05; IL-23: p(RB6-8C5) = NS; p(1A8) = 0.03.