Histologic examination of lungs from SCID mice receiving Th1, Th2, and Th0 cells. (a) Lung tissue from control SCID mouse that received intranasal OVA but no Th cells. H&E, ×250. Inset: High-power magnification of normal bronchiolar epithelium. H&E, ×400. (b) Lung tissue from SCID mouse that received Th2 cells and intranasal OVA. Peribronchiolar mononuclear cell infiltrates are noted. The airway lumen is filled and expanded by thick mucus. H&E, ×250. Inset: High-power magnification of the airway epithelium showing tall columnar cells exhibiting abundant cytoplasmic mucin and a collarette of inflammatory cells. H&E, ×400. (c) Lung tissue from SCID mouse that received Th1 cells and intranasal OVA. Dense peribronchiolar inflammatory infiltrates are seen. The airway lumen does not contain mucus plugs. H&E, ×250. Inset: Lymphocytes are penetrating the airway epithelium and surrounding tissue spaces. H&E, ×400. (d) Lung tissue from control SCID mouse that received Th1 cells but not intranasal OVA. The bronchiole is normal with rare mononuclear cells in the peribronchiolar tissue; H&E ×250. Inset: The airway epithelium is normal. H&E, ×400. (e) Lung tissue from SCID mouse that received Th0 cells and intranasal OVA. Peribronchiolar infiltrates are noted, and the lumen is filled with mucus; scattered inflammatory cells are noted. H&E, ×250. Inset: The airway epithelium resembles that of mice that received OVA-specific Th2 cells, with the presence of tall columnar cells with abundant cytoplasmic mucin (b). (f) Lung tissue from SCID mouse that received both Th1 and Th2 cells and intranasal OVA. Significant airway inflammation is noted, without airway mucus. H&E, ×250. Inset: The epithelium displays reactive-appearing columnar cells, with inflammatory cells at the bases. H&E, ×400. H&E, hematoxylin and eosin; SCID, severe combined immunodeficiency.