F4/80 staining indicates the Neu-YB strain recruits more macrophages into the tumor parenchyma. (A) F4/80 staining was quantified by using a 40× lens objective and counting the number of F4/80-stained macrophages per field (n = 3 tumors per strain and 10 random fields per tumor). Data shown are means and SEM. *P < 0.05, **P < 0.005, ***P < 0.0005 by t-test. (B) Representative fields of F4/80 staining taken at low magnification (scale bar = 200 μm) (i) and high magnification (scale bar = 25 μm) (ii). Neu-NDL = Neu deletion mutant (activated receptor).