Crosstalk between macrophages in the tumor microenvironment and malignant cells has been implicated during the pathogenesis of many kinds of tumors. However, role of lymphoma-associated macrophages in the progress of lymphoma as well as its underlying mechanism is far from completely clear yet. Here we evaluated the effect of lymphoma-associated macrophages on the characteristics of diffuse large B-cell lymphoma (DLBCL). Immunohistological staining demonstrated that level of CD163 positive macrophages, so called M2 type macrophage, was negatively related with the prognosis of DLBCL. In addition, M2 macrophage overexpressed asparaginyl endopeptidase legumain, as shown by double-immunofluoresence staining. Then we set up human DLBCL xenograft model. Mice were sacrificed at the different stages of tumor progress (average volume are 0.8 or 1.4 cm3. respectively. n=4). Real-time PCR results showed that mRNA expression of CD206 (M2 macrophage marker in mouse model) and legumain significantly increased with the progress of tumor. However, contents of matrix significantly decreased as indicated by sirus red and Masson's staining. Overlapping existed in immunofluorescence staining of legumain and fibronectin/ collagen I. In vitro, we cultured monocytes U937 with supernatant from primary DLBCL cells. Real-time PCR and western blot demonstrated that mRNA and protein expression of M2 markers as well as legumain significantly increased in U937 after incubation of 48 hours. Further, we cultured the legumain overexpressed stable cell line in the wells coated with fibronectin or collagen I. Western blot showed that compared to control, legumain overexpression promoted the degradation of fibronectin and collagen I. Mice in human DLBCL xenograft model were randomly received clodronate liposome; PBS liposome or legumain inhibitor via i.v. injection (n=5). The results revealed that tumor growth was significantly delayed in the clodronate liposome group compared with PBS liposome control. Similarly, injection of legumain inhibitor mimicked the effect of clodronate liposome on the tumor progress. Our data suggests that lymphoma-associated macrophages polarized by lymophoma cells promote tumor progress and this effect might be mediated by degrading the matrix via overexpressed legumain.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3535. doi:1538-7445.AM2012-3535