Fig. 1

CTLA-4 protein expression in tonsillar and HNSCC tissue. Immunohistochemical staining of CTLA-4 in a tonsil (a in tenfold magnification, b in 20-fold magnification), tumor-associated squamous epithelium (c in tenfold magnification, d in 40-fold magnification) and exemplarily in four HNSCCs (e–h in 20-fold and 40-fold magnification, respectively). CTLA-4-expressing lymphocytes are present in tonsillar tissue (a, b). Keratinocytes of tumor-associated squamous epithelium show strong cytoplasmic and weak nuclear CTLA-4 expression (c, d). HNSCC with predominantly CTLA-4-positive lymphocytes. The keratinizing tumor nests show strongly CTLA-4-positive (cytoplasmic) centers and CTLA-4-negative peripheral tumor cells (e). HNSCC with similar CTLA-4 expression pattern compared to e and an additional nuclear expression by tumor cells (f). HNSCC with weakly CTLA-4-positive tumor and immune cells and sporadic strong positive lymphocytes (arrows, g). HNSCC with CTLA-4-positive tumor cells (nuclear and cytoplasmic) (h)