IL4I1 expression in secondary lymphoid tissues and antigen-presenting cells. (A) Formalin-fixed paraffin-embedded hyperplastic tonsils (top row) or inflammatory lymph node (bottom row) tissue sections were stained with anti-IL4I1 polyclonal antibody and photographed at 20 × (left) and 100 × original magnification (right). (B) Different cell populations were isolated from blood and cultured as described in “Materials and methods” prior to mRNA extraction, and hIL4I1 RNA was measured by quantitative RT-PCR. Relative expression of hIL4I1 compared with a normal lymph node is shown. Mean ± SD from 3 independent experiments is shown. (C) Immunohistochemical analysis of mock-HEK, hIL4I1-HEK, MedB-1, and SU-DHL-4 cells, immature dendritic cells (iDCs), and mature dendritic cells (mDCs) was performed on paraffin-embedded cells using an anti-IL4I1 antibody. Arrows indicate positive cells. Note that most mDCs stained positive for IL4I1, whereas only rare iDCs disclosed a weak staining (arrow). (Inset) HLA-DR staining of the DCs indicating differential maturation. (D) HEK and DC populations were cultured in a reaction mixture with or without phenylalanine and secreted activity was evaluated by H₂O₂ measurement on the supernatant after 6-hour incubation at 37°C in 5% CO₂. Data are expressed as H₂O₂ production per 6 hours after subtraction of values obtained without phenylalanine. A representative experiment (of 3) is shown.