CD40 and glioblastoma: Furthermore, flow cytometry analysis of tumor-derived single cells showed that genetic IL-6 ablation abrogated CD40 expression in tumor Mφs, as indicated by a decrease in CD40+F4/80+ cell population but not in CD40−F4/80+ cell population (Fig. 3i), suggesting that IL-6 is critical for positively controlling Mφ expression of CD40 in the GBM microenvironment.