Objective:To study mechanisms by which human gliomas may escape immune surveillance. Methods: The effect of supernatant (SN) obtained from cultured media of malignant glioma cell lines on the proliferation of phytohemagglutinin-p stimulated peripheral blood lymphocytes (PBLs) from healthy subjects and patients with gliomas was examined by MTT assay. The immunosuppressive factor which might be existed in the SN was identified by neutralization method with specific antibodies and Northern blot hybridization of glioma cells.In addition, the cellular immunity of patients with gliomas and relevant hormone and catecholamine were determined. Results: It was found that the malignant glioma cells could release an immunosuppressive factor in an autocrine fashion which was further identified as the transforming growth factor β2 (TGF-β2). It was also demonstrated that the plasma levels of norepinephrine in glioma patients were significantly reduced and correlated well with the suppression of the patients' own cellular immunity. Conclusions: Two distinct mechanisms by which human gliomas may evade immune surveillance: 1.The secretion of an immunosuppressive factor which was identified as TGF-β2; 2. The dysfunction of NeuroImmune modulation in the presence of cerebral gliomas.