Diagnostic significance of histiocyte-related markers in malignant histiocytosis and true histiocytic lymphoma

Interrelationships of immunologic and enzymatic markers of histiocytes have been studied in malignant neoplasms of histiocytic/monocytic origin and in differential diagnostically relevant, large cell non-Hodgkin's lymphomas. Cryostat sections required for demonstrating cell surface antigens by monoclonal antibodies are inadequate for studying cellular detail, enzymatic maturation by alpha-naphthyl acetate esterase (ANAE), and demonstrating the classical cytoplasmic markers of histiocytes like lysozyme, alpha-1-antitrypsin (AT), and alpha-1-antichymotrypsin (ACT). These markers have been compared in gently fixed and vacuum paraffin-embedded material. The reactivity for monoclonal anti-human monocyte 1 (Mo 1) has also been preserved by this method. Malignant histiocytosis (MH) is characterized by a heterogeneous cell population. The mature, ANAE-positive cells with macrophage morphology usually show a diffuse cytoplasmic positivity for AT and ACT. Lysozyme is moderately positive to negative in these cells, but it is more efficient than these markers in revealing smaller cells resembling monocytes by focal positivity in the cytoplasm. The expression of Factor XIIIa (F-XIIIa) is connected with the phagocytic activation of histiocytic cells. F-XIIIa positive cells usually form a minority of the neoplastic population in MH, but the large cytophagocytic marcophages are invariably positive. Reactive macrophages in large cell non-Hodgkin's lymphomas are characterized by a coexpression of ANAE, AT, ACT, lysozyme, F-XIIIa and Mo 1. Typical cases of true histiocytic lymphoma (THL) are made up of a homogeneous population showing the above mature, phagocytizing phenotype. In MH, Mo 1 and ANAE recognize different subpopulations. The reciprocal relation of these markers is an abnormal phenotypic feature. The results presented in this article prove the diagnostic value of ANAE and lysozyme in confirming the histiocytic differentiation of malignant cells. Monoclonal anti-human monocyte 1 is useful for identifying the immature component in MH. Factor XIIIa can be considered a functional marker of mature phagocytic histiocytes and an aid in the diagnosis of THL.