The distribution of CD164 class I and II epitopes in postnatal tissue sections.

105A5 class I Mab staining of frozen sections of human child tonsil (A, B, K, M) and thymus (D, E, L, N) is compared with 103B2/9E10 class II Mab staining of tonsil (F, G) and thymus (I, J, O, P). Staining of tonsil using the immunoperoxidase technique revealed a sub–pan-reactive labeling with 105A5, with lymphoid cells and macrophages positive (A), while with 103B2/9E10 only the endothelia are stained (F). Dual immunofluorescence with the 105A5 (B, D, E), 103B2/9E10 (G, I, J), or isotype-matched mIgM (C) or mIgG3 (H) Mabs (green) and anticytokeratin (red) demonstrates that the basal layer epithelium of tonsil (G) and the subcapsular epithelium of thymus (I) coexpress the 103B2/9E10 epitope and cytokeratin, while medullary epithelium are cytokeratin-positive but 103B2/9E10-negative (J). Cytokeratin-positive epithelia in tonsil (B) and in the thymic subcapsular (D) and medulla (E) were 105A5-negative. 105A5 (red) clearly stained CD68- (green) positive macrophages in tonsil (K) and in the thymus, as illustrated for these cells at the corticomedullary junction (L). Strong double staining of CD43-positive cells (red) with 105A5 (green) and an absence of staining of blood vessel endothelia confirmed that the sub–pan-reactive staining observed with the immunoperoxidase method (A) included T cells but not endothelia (M). This was in contrast to dual labeling of thymic medulla, where cells expressed CD43 strongly but showed weak and often patchy staining with 105A5 (N). These dual-labeled cells were macrophages. In contrast to 105A5 expression, 103B2/9E10 (green) was weakly coexpressed on CD31- (red) positive blood vessel endothelia in thymus, while macrophages stained strongly with 103B2/9E10 but not with CD31 (P). In hyperplastic thymus (O), both CD31 (red) and 103B2/9E10 (green) were coexpressed on high endothelial venules. Original magnifications: (A, F) ×80; (B-E, G-J, M, N) ×240; (K, L) ×500; (O, P) ×600.