Tumor-associated macrophages increase the proportion of cancer stem cells in lymphoma by secreting pleiotrophin.

Tumor-associated macrophages (TAMs) are closely related to the occurrence and development of lymphoma, but their mechanism is still unclear. Here we collected peripheral blood and lymphoma tissue from patients with diffuse large B lymphoma. Results showed that the proportion of TAMs in high risk group was significantly higher than that in low-risk group. Moreover, the expressions of pleiotrophin (PTN), PTPRZ1 (PTN receptor) and beta-catenin in lymphoma tissues of high-risk group were also significantly higher than those in low-risk group. Correlation analysis showed that the proportion of TAMs in lymphocyte was positively correlated with the expression of PTN and PTPRZ1 in lymphoma tissue. In vitro experimental results showed that TAM promoted the invasion and proliferation of lymphoma cells by secreting PTN. We also found that TAMs increased the proportion of cancer stem cells in lymphoma. Animal experiments showed that TAMs promoted lymphoma growth. Both Ki-67 proliferation index and CD44+cancer stem cells increased significantly in TAM group. Blocking PTN or beta-catenin partly inhibited these effects of TAMs. In conclusion, TAMs increased the proportion of cancer stem cells through PTN/beta-catenin pathway in lymphoma.