Chitinase-3-like 1 immunohistochemistry in DLBCL. The immunoperoxidase complexes were visualized with diaminobenzidine (brown), and the sections were counterstained with hematoxylin. (A) PCNSL: original magnification ×200. Most tumor cells express moderate levels of CHI3L1 with a minority expressing strong levels. The largest profiles with heavy immunoreactivity are possibly astrocytes (see also panel D). (B) Nodal DLBCL: original magnification ×200. Most of the tumor cells contain low levels of immunoreactivity. The larger, strongly positive cells may be macrophages. (C) Extranodal DLBCL (spleen): original magnification ×200. (D) PCNSL: original magnification ×400. This is a higher power view of the PCNSL shown in panel A, showing astrocyte-like profiles with moderate to strong levels of immunoreactivity.