CXCL1 and escherichia coli infection: Interestingly IL-8, IL-6 and CXCL-1 are released by macrophages, the largest resident immune cell population in the bladder, and the urothelium.62 Early in pathogenic E. coli infection, shedding of superficial urothelial cells helps clear bacteria, but also exposes deeper layers of the urothelium, triggering cytokine release.