Antibody-dependent tumor cell growth inhibition by IL-10–polarized M2-like macrophages. (A) CFSE-labeled HOS-143b cells coated with anti-EGFR cetuximab or non-binding anti-CD20 rituximab were incubated with IL-10–stimulated M2-like macrophages for two hours. Cell conjugate formation was evaluated by flow cytometry, assessing CD32+ macrophages acquiring high CFSE fluorescence of the tumor cells. Representative data of two experiments are depicted. (B) In one experiment, CD32+CFSE+ cells (upper right quadrant in lower panel A) were sorted by flow cytometry and examined by Immunofluorescence microscopy, detecting HLA-DR-stained macrophages in red (lower left), CFSE+ tumor cells in green (lower right) and DAPI-stained cell nuclei in blue (upper right) and composites (upper left). (C) HOS-143b (n = 4–7) and (D) sOHS (n = 5–8) cells were coated with cetuximab (hatched pattern) or rituximab (control, no pattern) and incubated with M2-like macrophages pre-stimulated with or without IL-10. After two days tumor cell numbers were analyzed by ANOVA and Dunnett’s post test.