Cytokine Profiles and the Effect of Intravitreal Aflibercept Treatment on Experimental Choroidal Neovascularization

Role of microglia/macrophage polarisation in intraocular diseases (Review)

Macrophages form a crucial component of the innate immune system, and their activation is indispensable for various aspects of immune and inflammatory processes, tissue repair, and maintenance of the balance of the body's state. Macrophages are found in all ocular tissues, spanning from the front surface, including the cornea, to the posterior pole, represented by the choroid/sclera. The neural retina is also populated by specialised resident macrophages called microglia. The plasticity of microglia/macrophages allows them to adopt different activation states in response to changes in the tissue microenvironment. When exposed to various factors, microglia/macrophages polarise into distinct phenotypes, each exhibiting unique characteristics and roles. Furthermore, extensive research has indicated a close association between microglia/macrophage polarisation and the development and reversal of various intraocular diseases. The present article provides a review of the recent findings on the association between microglia/macrophage polarisation and ocular pathological processes (including autoimmune uveitis, optic neuritis, sympathetic ophthalmia, retinitis pigmentosa, glaucoma, proliferative vitreoretinopathy, subretinal fibrosis, uveal melanoma, ischaemic optic neuropathy, retinopathy of prematurity and choroidal neovascularization). The paradoxical role of microglia/macrophage polarisation in retinopathy of prematurity is also discussed. Several studies have shown that microglia/macrophages are involved in the pathology of ocular diseases. However, it is required to further explore the relevant mechanisms and regulatory processes. The relationship between the functional diversity displayed by microglia/macrophage polarisation and intraocular diseases may provide a new direction for the treatment of intraocular diseases.

Transcriptional and Distributional Profiling of Microglia in Retinal Angiomatous Proliferation

Macular neovascularization type 3, formerly known as retinal angiomatous proliferation (RAP), is a hallmark of age-related macular degeneration and is associated with an accumulation of myeloid cells, such as microglia (MG) and infiltrating blood-derived macrophages (MAC). However, the contribution of MG and MAC to the myeloid cell pool at RAP sites and their exact functions remain unknown. In this study, we combined a microglia-specific reporter mouse line with a mouse model for RAP to identify the contribution of MG and MAC to myeloid cell accumulation at RAP and determined the transcriptional profile of MG using RNA sequencing. We found that MG are the most abundant myeloid cell population around RAP, whereas MAC are rarely, if ever, associated with late stages of RAP. RNA sequencing of RAP-associated MG showed that differentially expressed genes mainly contribute to immune-associated processes, including chemotaxis and migration in early RAP and proliferative capacity in late RAP, which was confirmed by immunohistochemistry. Interestingly, MG upregulated only a few angiomodulatory factors, suggesting a rather low angiogenic potential. In summary, we showed that MG are the dominant myeloid cell population at RAP sites. Moreover, MG significantly altered their transcriptional profile during RAP formation, activating immune-associated processes and exhibiting enhanced proliferation, however, without showing substantial upregulation of angiomodulatory factors.

Aqueous humor cytokine levels through microarray analysis and a sub-analysis based on optical coherence tomography in wet age-related macular degeneration patients

Background

To identify disease-specific cytokine and growth factor profile differences in the aqueous humor between wet age-related macular degeneration (AMD) patients and age-matched controls and to correlate their levels with the optical coherence tomography (OCT) findings.

Methods

Aqueous humors were obtained from 13 wet AMD eyes and 10 control eyes. Twenty cytokines and growth factors were measured using a RayBio antibody microarray technology in wet AMD and control eyes.

Results

The samples obtained from wet AMD patients exhibited a significantly increased expression of MCP-1, MIP-1α, MIP-1β, and vascular endothelial growth factor (VEGF). Subretinal fluid (SRF) patients showed significantly lower levels of proinflammatory cytokines, such as IL-1α and GM-CSF, than those without SRF. Pigment epithelial detachments (PED) patients showed lower levels of inflammatory cytokines, such as GM-CSF, IFN-γ, and TNF-α, than those without PED. Subretinal tissue (SRT) patients showed a higher level of IFN-γ than those without SRT. Compared with the controls, type 1 macular neovascularization (MNV) patients showed increased levels of MCP-1, MIP-1α, and MIP-1β, but not VEGF (p = 0.083). However, type 2 MNV patients showed increased levels of MCP-1 and VEGF (p = 0.040 and p = 0.040).

Conclusion

Inflammatory cytokines varied according to the type of AMD- and OCT-based parameters. Our observation of low levels of VEGF in patients with type 1 MNV implies that the inhibition of VEGF alone appears to be insufficient treatment for these patients and that cytokines such as MCP-1, MIP-1α, and MIP-1β should be modulated. And the presence of SRF in MNV may be associated with a positive prognosis because we found relatively low levels of proinflammatory cytokines.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12886-021-02152-6.