CD4 and meningioma: To detect the infiltration of immune cells in three grades of meningioma tissues, immunohistochemistry was performed and the results showed that the infiltrated immune cells in WHO grade III meningioma was mainly composed of CD68+ macrophages (P = 0.006) accompanied by a significant decrease of CD3+ (P = 0.008), CD4+ (P = 0.003) and CD8+ (P = 0.038) T lymphocytes compared with WHO grade I and WHO grade II meningioma (Fig. 2A-D and Table 3).