Myeloid cells are one of the key regulators of inflammatory and immune responses. A chemoattractant receptor CXCR2 has been reported to possess contradictory roles in tumourigenesis depending on the tissue type and stage of progression. The role of Cxcr2 in bladder tumourigenesis is largely unknown. Here we sought to investigate the effects of Cxcr2 deletion on myeloid cells recruitment and the initiation and progression of bladder tumour in mice.
Bladder tumours were induced by 0.05% (v/v) 4-Hydroxybutyl(butyl)nitrosamine (OH-BBN) in drinking water for 10 weeks. Mice used were; C57BL/6 (wt), LysMCre Cxcr2fl/fl (Cxcr2 flox) in which Cxcr2 was deleted in myeloid cell lineage, and Cxcr2-/- (Cxcr2 ko) in which Cxcr2 was deleted in the whole body. Bladders were harvested at 2 and 20 weeks from the first administration of OH-BBN. Histopathological analysis and neutrophils infiltration were evaluated by H&E staining. Macrophages and T-cells infiltrations were determined by immunohistochemistry using F4/80, CD3, CD4, CD8 and FoxP3 antibodies.
Significant increase in the tumour occurrence was observed in Cxcr2 flox, but not in Cxcr2 ko. Tumours in Cxcr2 flox mice were also more progressed compared to wt. Cxcr2 flox showed a reduction in stromal thickness, accompanied by the decrease in neutrophils and macrophages at 2 weeks from the start of carcinogen induction, as expected as a consequence of Cxcr2 deletion. Interestingly, T-cells infiltrations were also reduced in Cxcr2 flox bladders. Unexpectedly, at a later stage, Cxcr2 flox tumours were highly infiltrated with neutrophils. Furthermore, Cxcr2 flox tumours were also highly infiltrated with T cells, particularly with CD3+ and CD8+ populations. This may suggest that an immune response has been locally triggered by the tumour cells and that this effect is independent of the role of Cxcr2 as a chemoattractant for neutrophils.
In conclusion, (1) Cxcr2 deletion enhanced bladder tumorigenesis, (2) acute inflammatory and immune responses were suppressed in the Cxcr2-dependent manner, and (3) in tumours, neutrophils and T cells were recruited into the tumour area regardless of the lack of Cxcr2. These results suggest that tumours may have developed a strong compensatory mechanism to Cxcr2 signalling in recruiting neutrophils in the bladder. We propose that Cxcr2 could be a potential translational target for invasive bladder cancer that can be combined with current immunotherapy.
