CD68 and neoplasm: Through immunostaining with antibodies against human CD3 (T lymphocyte), CD20 (B lymphocyte), CD45 (histiocyte), CD68 (macrophage), and lysozyme, it was found that the cells in the PNs of the mice with human U937 tumor were strongly immunoreactive to lysozyme and modestly immunopositive for CD45 and CD68.