Fig. 5.

CD11b⁺Gr-1⁺ myeloid cells in lungs metastatic niche promote cancer cell colonization. a CXCL17 increased cancer cell extravasation into the lungs of mice. Athymic nude mice were treated with recombinant CXCL17 protein (1 μg/mouse, 2 times/week, n = 6 per group) for 14 days; MDA-MB-231-RFP-Luc cells were injected into mice by tail vein. The lungs of these mice were harvested after 48-h injection, then examined by a confocal microscope. b Scheme of CD11b⁺Gr-1⁺ depletion in the animal model. Depletion of CD11b⁺Gr-1⁺ cells decreased CXCL17-mediated cancer extravasation (c) and tumor nodules formation (d) in the lungs of mice. e The H&E staining of tumor sections of lungs. For MDSC depletion studies, mice (n = 6 per group) were treated with isotype or anti-Gr-1 antibodies (Bio X Cell) at 100 μg/mouse intraperitoneal injections every 4th day, and 4T1 cells were injected via tail vein into the mice (n = 6 per group). The control group received intraperitoneal injection of purified rat immunoglobulins. PKH26-labeled 4T1 cells were injected into mice by tail vein for indicated times (24 days for lung metastasis and 48 h for extravasation). The lungs of these mice were harvested and examined by a confocal microscope. Each value is the mean ± SEM; *p < 0.05. White arrows indicate cancer cells