Expression of phosphorylated STAT proteins in normal lymphoid tissue.

Expression of P-STAT6 (A), P-STAT3 (B), and P-STAT5 (C) was examined by immunohistochemistry in formalin-fixed sections of a reactive human tonsil. P-STAT6 and P-STAT5 demonstrated low basal levels of expression, with rare nuclear staining of lymphocytes (arrows) outside of the germinal center (GC). Basal levels of P-STAT3 were significantly higher, with numerous positive cells within and outside of the GC. Original magnifications, × 500.