MPO suppresses DC Ag uptake/processing and migration to LNs. The frequency of DCs (CD11c^hi cells; flow cytometry) in draining LNs of WT (n = 8) and Mpo^−/− mice (n = 8) 18 hours after subcutaneous OVA/LPS (Ai) or OVA/CFA (Aii) injection or (Aiii) OVA/LPS-injected WT mice receiving DMSO (n = 8) or ABAH (n = 8). (B) BM-derived CD45.1⁺ DCs (+OVA/LPS) were injected subcutaneously into CD45.2⁺ WT (n = 6) and Mpo^−/− recipients (n = 6). Accumulation of the transferred DCs in draining LNs was assessed 18 hours later (flow cytometry). (C) CCR7 expression (flow cytometry) on BM-derived murine DCs cultured (18 hours) with LPS (1 μg/mL), H₂O₂ (100 μM) and (Ci) with or without supernatant (5% v/v) from CB/fMLP-degranulated WT or Mpo^−/− neutrophils or (Cii) increasing doses of purified mouse MPO. Dotted line represents unstimulated DCs. (Ciii) Representative flow cytometry plots showing LPS-induced DC CCR7 expression in the absence or presence of mouse MPO (0.0625 μg/mL). (D) DQ-OVA uptake/processing (flow cytometry) by BM-derived murine DCs cultured (2 hours) with DQ-OVA (which exhibits green fluorescence upon proteolytic degradation) and LPS/H₂O₂ in the presence or absence of mouse MPO (0.125 μg/mL). (E) WT (n = 6) and Mpo^−/− mice (n = 6) were injected subcutaneously with DQ-OVA (50 μg) and LPS (30 μg). Uptake/processing of DQ-OVA by DCs was assessed in draining LNs 4 hours later (flow cytometry). Data are representative of 2-3 independent experiments. Each group in (C-D) contained 4 replicates. *P < .05, **P < .01, ***P < .001.