TLR4 and TRIF are necessary for feedback granulopoiesis. (A) Plasma G-CSF levels in control and antibody treated C57BL/6 (n = 3, each), TLR4^−/− (n = 3, each), MyD88^−/− (n = 5, each), and TRIF^−/− mice [n(1A8) = 5, n(PBS) = 4]. Note the significant increase of G-CSF in C57BL/6 and MyD88^−/− and nonsignificant changes in the TLR4^−/− and TRIF^−/− mice. p(C57BL/6) = 0.04; p(TLR4^−/−) = NS; p(MyD88^−/−) < 0.001; p(TRIF^−/−) = NS. (B) Absolute marrow cell numbers in TLR4^−/− hind limbs after 8 days of 1A8-induced neutropenia. Note the insignificant changes of LSK, GMP, and MEP (n = 3). p(LSK, GMP, CMP, and MEP) = NS. (C) Absolute cell numbers in hind limbs of n = 5 MyD88^−/− mice. LSK and GMP are significantly increased in neutropenia. p(LSK) = 0.03; p(GMP) = 0.02; p(CMP) = NS; p(MEP) = 0.03. (D) Hind limb marrow cell numbers of n = 5 TRIF^−/− mice after 8 days of 1A8-induced neutropenia versus PBS (n = 4). Although there is an increase of LSK, changes at progenitor level are nonsignificant. p(LSK) = 0.02; p(GMP) = NS; p(CMP) = NS; p(MEP) = NS.