E, F. Frequencies of CD4+ and CD8+cells producing the proinflammatory cytokine IFNγ were found among the tissues of tumor-bearing mice in the MC38 modelby intracellular cytokine staining Kralovics et al(, 2005) and flow cytometry after ex vivo re-stimulation of recovered leukocytes by PMA and ionomycin in the presence of brefeldin A. 