The cause of IMH is generally considered to be unrelated to ocular inflammation [9, 10]. But after IMH onset, due to tissue damage and reparation, it often leads to local inflammatory reactions in eyes, resulting in changes in the levels of related cytokines in the aqueous humor. The degree of ocular inflammatory response and changes in cytokines in the aqueous humor are positive for the treatment, prognosis and diagnosis of IMH.
In the normal retina, Muller cells penetrate the neurosensory layer, and its fibers extend from the outer membrane to the inner limiting membrane, acting as a retinal support and nutrient metabolism. After the formation of IMH, the retina undergoes a process called reactive gliosis [11]. This is an event triggered by damage involving the penetration of most activated astrocytes. Activation of the intermediate filament protein glial fibrillary acidic protein and vimentin is critical for the formation of glial scars[12, 13].
On the retina, Muller glial cells are the major glial cell type of reactive scar formation following disease-induced retinal degeneration[14]. Muller cells and glial cells in the retina may migrate to the outer surface of the inner limiting membrane under the action of various inflammatory factors to restore nutrients Some researchers believe that the proliferation and contraction of these cells on the inner limiting membrane results the increasing of the holes. After the formation of macular hole, lymphocytes can destroy the blood-retinal barrier and migrate into the vitreous cavity, where lymphocytes contact with the transitional pigment cells and glial cells, and secrete cytokines, promote inflammatory response as well as enhance phagocytosis of macrophages [15]. Moreover, lymphocytes in vitreous cavity also promotes the transformation of glial cells into fibroblasts and accelerates the repair of tissue proliferation [16].
As we know, immune system-mediated inflammatory responses play an important role in injury-induced neurological damage and tissue repair. The inflammatory response during trauma is mainly induced by innate immune cells, including microglia and astrocytes which plays an important role. However, the recruitment of these innate immune cells leads to the recruitment of T cells and other immune cells to some extent, and finally induces apoptosis and repair of damaged sites [17].
In this study, it can be seen that there is a significant up-regulation of the expression of GM-CSF which is an important component of microglial products. As a type of macrophage, microglia can phagocytose the debris of damaged cells and accompany the release of various cytokines. In the case of idiopathic macular hole, the microglia in the damaged macular area is rapidly activated, which causes the microglia morphology to transform into an "ameboid"-like state and migrate to the injury site, followed by release of various cytokines including nerve growth factor (NGF), protective cytokine (IL-4), immunosuppressive cytokine (IL-10), as well as NO and ROS, followed by the production of pro-inflammatory cytokines such as IL-1, IL-6 and IFN-γ[18]. These above mentioned cytokines might accumulate in the aqueous humor and could be detected as described in our study. Accordingly, the results of this study verified that the above mentioned cytokines were significantly up-regulated in comparison with the control group, and GM-CSF was associated with many of the cytokines, including GM-CSF and IL-1 (r = 0.67904, p < 0.001), and IL-4 (r = 0.76017, p < 0.001), and IFN-γ (r = 0.59922, p = 0.004097), which to some extent indicates that microglia do play an important role in the immune response of the IMH .
After the microglia are activated and produce the cytokine IL-1, astrocytes/Miller cells are subsequently activated. In such adaptive nerve injury of macular hole, Miller cells can produce cytokines such as NGF and HGF to promote neuron survival. In this study, it can be seen that both NGF and HGF are significantly up-regulated in comparison with the control group, and NGF is associated with HGF (r = 0.64951, p = 0.001441). As we know that HGF and NGF play an important role in the treatment of ocular nerve injury diseases, including corneal damage, glaucoma and the like. So we hypothesized that HGF and NGF can also play an important role in tissue repair during the prophase an postoperative treatment recovery of the macular hole [19] .
In this study, the method of multiple magnetic beads immunization was used to detect the changes of cytokine concentration in the aqueous humor of patients with IMH. Compared with the traditional ELISA method, this method can detect more kinds of cytokines with fewer samples. Moreover, multiple immunomagnetic beads are used to simultaneously detect 48 cytokines in a single experiment, which can well avoid the interference of instability caused by batch effects [20].