Figure 4. Neutrophil depleted mice display increased numbers of monocyte and dendritic cell progenitors within their bone marrow owing to a dysregulated IL-23 – IL-17 – G-CSF axis.

Balb/c mice were administered HDM or PBS intranasally (i.n.) 3 times per week for 1 week. At 24 hours prior to each HDM/PBS administration, mice were treated with either 100 μg of neutrophil depleting antibody, 1A8, or isotype control antibody, 2A3 intraperitoneally (i.p). At 24 hours post final HDM/PBS exposure, BALF, lung tissue, blood and bone marrow were collected. (A) The number of Ly6C^low and Ly6C^high monocytes in the blood were quantified by flow cytometry. (B) The percentage of monocyte dendritic cell progenitors (MDPs) and common dendritic cell progenitors (CDPs) within the bone marrow were assessed by flow cytometry. (C) The concentration of G-CSF in the serum, lung homogenate and BALF was determined by ELISA. Expression of Csf3 (G-CSF gene; D), Il17 (E) and Il23 (F) was assessed in whole lung by qPCR. (G) Schematic depicting the negative feedback pathway by which tissue neutrophils limit granulopoiesis by modulation of the IL-23 – IL-17 – G-CSF axis. Figures present data from 2 independent experiment with 4-6 mice per group in each experiment. Results depicted as mean ± SEM. *P<0.05, **P<0.01, ***P<0.001, ****P<0.0001 using Mann–Whitney statistical test.