Immunohistochemical detection of HLA-DR and CD8. Photomicrographs demonstrating immunohistochemical detection of HLA-DR (A,C,E) and CD8 (B,D,F). Panels A and B demonstrate an HLA-DR⁺ case with brisk CD8⁺ cytotoxic T-cell response. Panels C and D show an HLA-DR^- case with few CD8⁺ tumor-infiltrating lymphocytes. Panels E and F demonstrate a microarray HLA-DRA^- case that has staining for the protein in an unusual cytoplasmic pattern. This case also demonstrates low numbers of CD8⁺ cytotoxic T cells, indicating possible aberrant protein localization or function. Original magnification, ×100.