Exposure to FA21 MWCNT exacerbates HDM-induced allergic lung inflammation and promotes cysLT production. To examine the effect of MWCNT exposure on pre-existing allergic airway inflammation, C57BL/6 mice (4–6 per group) were intranasally challenged with PBS (control) or HDM allergen over a 2-week period (on days 0, 7, and 14) to induce allergic inflammation and then exposed to FA21 MWCNT (50 μg) on day 15 by intratracheal administration. BALF and lung tissue were collected 24 h after MWCNT administration on day 16 for analysis of pulmonary inflammation (as illustrated in the experimental design in Figure 1 ). Groups comprised of mice treated with FA21, HDM, or FA21 + HDM. Control mice were treated with carrier alone. (A) BALF cell differential counts were determined and expressed as absolute cell number per mouse of lymphocytes (LYM), eosinophils (EOS), macrophages (MAC), and polymorphonuclear neutrophils (NEU). (B) Cell-associated EPO levels in the BALF were determined by colorimetric assay. (C) CD11b + <t>F4/80</t> - GR1 - Siglec-F + eosinophil numbers present in the BALF were analyzed by flow cytometry. (D) Peribronchial and perivascular inflammation was assessed by histological analysis of lung tissue sections stained with H E (20×). In addition, inflammatory cells infiltrating the airways were examined by microscopic evaluation and imaging of cytospin preparations of BALF cells stained using Hema3. (E) CysLT levels present in BALF determined by ELISA. Results are mean ± SEM ( n = 6), ∗∗ p