C3 and neoplasm: Here, we described that C3, the central factor of the complement system, was activated and released C3a in MB, and consistent with other publications, C3a activated astrocytes in vitro: C3a upregulated the expression of the astrocyte activation marker GFAP and some proinflammatory cytokines; C3a stimulated p38 MAPK pathway signal transduction in astrocytes; and C3a enhanced the tumor-promoting ability of astrocytes.