Immunohistochemical analysis of STAT1 expression levels in human breast cancers. (A) Immunohistochemical analysis on wild-type (WT) and STAT1-/- spleens to confirm the specificity of the antibody against STAT1. Sections of WT or STAT1-/- spleens were stained with a polyclonal rabbit antibody against an epitope in STAT1 which is homologous to both humans and mice. STAT1 reactivity was observed predominantly in the lymphoid cells of the white pulp in WT spleen. However, no appreciable signal was detected in the STAT1-/- spleen. Original magnification, 100×. Scale bars = 200 μm. (B) The staining intensity of the STAT1+ signal was evaluated by using a three-tiered scale (low, intermediate, and high). Low, intermediate, and high STAT1 correspond to the staining intensity scores of 1, 2, and 3, respectively, in Table 2. Six cases of estrogen receptor-alpha-negative (ERα-) and six cases of ERα+ primary human breast tumors are shown here as representative images. Original magnification, 200×. Scale bars = 100 μm.