CD4 and astrocytoma (excluding glioblastoma): Since HIV does not infect mouse cells as the viral envelope glycoprotein, gp120, does not engage mouse CD4 receptors (Browning et al., 1997), we propose that the microinjected human astrocytoma cells form GJs with resident mouse brain cells (Supplementary Figure S1 and Supplementary Data), and the cytoplasmic apoptotic factors generated in HIV-infected U87-CD4-CCR5 cells diffuse into uninfected host cells via Cx43 GJs and lead to their apoptosis.