DC activation in LNs is increased by MPO deletion or in vivo inhibition. MPO activity (Ai; assessed by measuring ΔA₄₆₀ upon oxidation of o-dianisidine dihydrochloride in the presence of H₂O₂) and neutrophil accumulation (Aii; flow cytometry) in draining LNs of normal (n = 4) and subcutaneously OVA/LPS-immunized WT mice receiving ABAH (n = 4) or DMSO (vehicle; n = 4). (B) DC activation (flow cytometry) 4 hours (Bi-ii) and 18 hours (Biii-iv) after subcutaneous OVA/LPS injection, in draining LNs of WT (n = 6/time point) and Mpo^−/− mice (n = 6/time point), and WT mice receiving ABAH (n = 6/time point). CD4 T-cell proliferation (Ci; intracellular Ki-67 staining; flow cytometry), activation (Cii; CD44 expression; flow cytometry), and IFN-γ production (Ciii; intracellular staining, flow cytometry) 3 days after OVA/LPS injection, in draining LNs of WT mice receiving DMSO (n = 6) or ABAH (n = 6). Data are representative of 2 independent experiments. *P < .05, **P < .01, ***P < .001.