Commensal germs and MyD88 are dispensable in G-CSF–mediated feedback. (A) Flow cytometry of peripheral blood from neutropenic GF C57BL/6 mice and controls (n = 3). (B) Absolute marrow cell numbers in both hind limbs of GF C57BL/6 mice. Note the similarity of changes in GF mice compared with SPF-kept C57BL/6 (n = 3). p(LSK) = 0.04; p(GMP) = 0.05; p(CMP) = NS; p(MEP) = NS. (C) Plasma G-CSF levels in C57BL/6 and GF mice after neutrophil depletion with 1A8 versus controls. Note the significant increase of G-CSF in neutropenic mice and decreased baseline G-CSF levels in GF mice compared with animals maintained under SPF conditions [n(GF) = 3, n(C57BL/6) = 3; p(C57BL/6) = 0.04; p(GF C57BL/6) = 0.02].