Neutrophils can also stimulate the macrophages to release IL-1b, a proinflammatory cytokine, which stimulates the release of neurotrophic factors, such as NGF and BDNF, that, in turn, induce new nerve fibers that are directly linked to endometriosis lesions, overstimulating the sensory neurons and causing pain [84-86]. Here, NGF is linked to endometriosis.