Reduced phagocytosis of apoptotic cells in malignant lymphoma

Efficient removal of lymphocytes undergoing programmed cell death (apoptosis) by macrophages plays an important role for the proper function of normal immune system. Furthermore, in malignant lymphoma, elimination of apoptotic tumor cells by phagocytes contributes to the anti-tumor immune response. It is unknown, however, whether macrophages in normal and malignant lymphoid tissues differ in their ability to recognize and remove apoptotic cells. Our present results demonstrate that normal and malignant lymphoid tissues differ according to the extent of the infiltration by macrophages. The highest densities of macrophages (p < 0.0001) were detected in diffuse large B-cell lymphoma, centroblastic (DLBCL-CB) and immunoblastic variants and Burkitt's lymphoma. The grade of the macrophage infiltration correlated with the proliferation rates of the tumors (p < 0.0001). Compared with normal lymphoid organs, malignant lymphoma contained lower percentages of apoptotic cells phagocytosed by tissue macrophages (p < 0.001). Of all lymphomas tested, mantle cell lymphoma and DLBCL-CB expressed the lowest percentages of phagocytosed apoptotic cells (p < 0.0001).