Human leukocyte populations in simple bronchial grafts and bronchus–PLN cografts.

Mature simple bronchial grafts (A-C) show dispersed CD45⁺ mucosal leukocytes (A), including tryptase⁺ mast cells (B, arrows) and CD68⁺macrophages (C, arrows). Bronchus–PLN cografts (D-L) show CD45⁺ leukocytes (D) dispersed in the mesenchyme and clustered in BALT (D, circled area). BALT cells (E, circled area) include mature CD20⁺ B cells (green fluorescence) and CD20⁺CD38⁺ (orange fluorescence) plasma cells. Some CD38⁺ plasma cells are found at the basal aspect of submucosal glands (F, arrows), allowing for transcytosis-mediated IgA secretion (G) into the gland lumen. CD3⁺ T lymphocytes are found within the epithelium (H, arrow) of bronchus–PLN cografts, among BALT cells (H, circled area) and are dispersed in the mesenchyme (I, arrows). Co-implanted PLNs stay well delimited (I-K, circled area) externally to the cartilage and show numerous CD3⁺ T lymphocytes (I), mature CD20⁺ B cells (green fluorescence), and CD20⁺CD38⁺ (orange fluorescence) plasma cells (J) and CD68⁺ macrophages (K). Human PLNs maintained long term in the SCID host also show evidence of proliferating Ki67⁺ leukocytes (L). Bar represents 100 μm in A, B, D, E, J; 250 μm in I, K; 50 μm in C, H; 25 μm in F, G, L. e indicates epithelium; g, gland; and c, cartilage. Original magnification ×50 (A, B, D, E, J); ×20 (I, K); ×100 (C, H); ×200 (F, G, L).