Flt3-L and Flt3-L receptor expression. (A) Flt3-L mRNA expression by different organs from B6 and CD11c.DOG after 2 daily injections of DT. Results are expressed as mean Ct (cycle threshold) value, that is, the number of PCR cycles required to obtain the half-maximal amount of amplified Flt3-L DNA starting from a fixed amount of total cDNA. High Ct values indicate low expression level of Flt-L mRNA, whereas low Ct values indicate high expression level. Error bars indicate SEMs (n = 6-10 mice). Lu indicates lung; LN, skin-draining lymph nodes; Sp, spleen; Th, thymus; Li, liver. (B) FACS histogram overlays showing expression of CD135 (Flt3, the Flt3-L receptor) by different spleen cell populations. Cell gates were set for cDCs (CD11c^hiMHC-II⁺), pDCs (CD11c^intPDCA-1⁺); pre-DCs (CD19⁻CD3⁻NK1.1⁻CD11b⁻MHC-II⁻CD45RA^−/intCD172a^intCD11c^int), B cells (CD19⁺), T cells (CD3⁺ NK1.1⁻), NK cells (CD3⁻NK1.1⁺), NKT cells(CD3⁺NK1.1⁺), macrophages (CD11b⁺MHC-II^−/loF4/80⁺), monocytes (SSC^loCD11b⁺Gr-1^int), granulocytes (SSC^hiCD11b⁺Gr-1^hi), and stromal cells (CD19⁻CD3⁻NK1.1⁻CD11c⁻CD11b⁻MHC-II⁻Ter119⁻CD45⁻). P < .01, ANOVA.