Glioma cell-derived placental growth factor induces regulatory B cells

Tumor specific immune regulatory cells play an important role in the pathogenesis of glioma. The mechanisms have not been fully understood yet. It is suggested that placenta growth factor (PlGF) is involved in the generation of immune regulatory cells. This study aims to investigate the role of glioma cell-derived PlGF in the generation of regulatory B cells (Breg). Glioma cells were isolated from surgically removed glioma tissue. Cytokines were measured by enzyme-linked immunosorbent assay, quantitative real time RT-PCR and Western blotting. Immune suppressor functions of Bregs were assessed by T cell proliferation assay. The results showed that glioma cells expressed PlGF, which was increased after a non-specific activation. Naïve B cells captured the PlGF to differentiate into transforming growth factor-β positive Bregs. The Bregs were activated upon exposure to protein extracts of glioma tissue to suppress the CD8(+) T cell proliferation and the release of perforin and granzyme B. We conclude that glioma cell-released PlGF can induce Bregs to suppress CD8(+) T cell activities.