Immune cell infiltration in xenograft tumors measured by immunohistochemistry. Mouse xenograft tumors treated with trastuzumab, single hinge cleaved trastuzumab (scIgG-T), and the isotype control were fixed in 4% paraformaldehyde. Six immunohistochemistry slides were prepared from the paraffin-embedded tissues of two mice from each treatment group. Monocytes/macrophages were stained using the anti-mouse integrin αM/CD11b and anti-mouse F4/80 antibodies. (A) Representative images (×40) of CD11b-stained tumor tissue and positive-stained immune cells indicated by black arrows. Right bar graph: average number of CD11b-positive cells per tumor tissue slide (n = 6). Pairwise t test used to compare different treatment groups. **P < 0.005. (B) Representative images (×40) of F4/80-stained tumor tissues from different treatment groups. Right bar graph: Average number of positive stained cells detected per tissue slides (n = 6). Pairwise t test used to compare different treatment groups. **P < 0.005.