Mapping of Fc gamma receptors in the human and porcine eye

Pathological consequences of anti-citrullinated protein antibodies in tear fluid and therapeutic potential of pooled human immune globulin-eye drops in dry eye disease

PURPOSE

To investigate the role of Anti-Citrullinated Protein autoantibodies (ACPAs) in the pathology of dry eye disease (DED) and the therapeutic potential of pooled human immune globulin-eye drops in these patients.

METHODS

We investigated the presence of citrullinated proteins and ACPAs in ocular surface wash (OSW) and conjunctival impressions from patients with DED and determined the pathological consequences of OSW with high ACPA using in vitro experiments and in vivo murine models. We performed a randomized, double-masked, pilot clinical trial to determine the safety, tolerability and preliminary efficacy of using pooled human immune globulin-eye drops to treat DED patients with ACPAs in OSW.

RESULTS

We found that neutrophils are a source of citrullinated proteins on the ocular surface of DED patients. We detected significantly higher immunoglobulin amount and presence of several species of ACPAs in OSW from DED patients. We also found that OSW with high ACPA contributes to production of NETs, and that ACPAs cause ocular surface disease in murine eyes, both of which are reduced with addition of Immune globulins. As compared to Vehicle treatment, pooled human immune globulin-eye drops (IVIG 4 mg/mL) twice a day for 8 weeks caused significant reduction in signs and symptoms of DED with no difference in tolerability or adverse events.

CONCLUSIONS

This is the first report demonstrating ACPAs in OSW of DED patients and their contribution to ocular surface disease. The first-in-human clinical trial suggests that pooled immune globulin-eye drops are a potential new class of biologic therapies for Dry Eye patients.

Effects of intravitreally injected Fc fragment on rat eyes

PURPOSE

Anti-vascular endothelial growth factor (VEGF) drugs are used to treat neovascular eye diseases. Some of these drugs contain Fc fragments (Fc), but it is unknown how their mode of action is influenced by Fc. Therefore, this study investigated the effects of Fc on rat eyes after intravitreal injection.

METHODS

Eighteen Long-Evans rats were intravitreally injected with sterile, biotin-labeled rat Fc (9.1 μg in 5 μl PBS). For control, 5 μl PBS was injected in another nine rats. Animals were sacrificed between 1 and 3 days (group 1), 7 days (group 2), and 14 days (group 3) after injection. The right eyes were examined by electron microscopy (EM). The left eyes were stained by immunohistochemistry to investigate the distribution of Fc and the presence of macrophages.

RESULTS

After 1 day, Fc had penetrated into the anterior chamber and the retina up to the inner nuclear layer, and was located especially in retinal vessels. High numbers of infiltrating cells were present within the vitreous, around the ciliary body, anterior chamber and inside the retina 1-3 days after Fc injection (p < 0.02 group 1 vs. control). Immunohistochemistry and EM showed that they were macrophages or granulocytes in close association with Fc. Ultrastructurally, there were effects on the blood vessels such as thrombocyte activation and fibrin formation.

CONCLUSIONS

Biotin labeling is ideal for investigating the distribution of intravitreally injected proteins in ocular tissue. Fc fragments at a dose corresponding to their concentration in standard AMD treatments induced inflammation, and particularly the attraction of immune-competent cells. This may be associated with the risk of inflammation or endophthalmitis after anti-VEGF treatment, and needs further investigation.

Cellular signaling and factors involved in Müller cell gliosis: neuroprotective and detrimental effects

Müller cells are active players in normal retinal function and in virtually all forms of retinal injury and disease. Reactive Müller cells protect the tissue from further damage and preserve tissue function by the release of antioxidants and neurotrophic factors, and may contribute to retinal regeneration by the generation of neural progenitor/stem cells. However, Müller cell gliosis can also contribute to neurodegeneration and impedes regenerative processes in the retinal tissue by the formation of glial scars. This article provides an overview of the neuroprotective and detrimental effects of Müller cell gliosis, with accounts on the cellular signal transduction mechanisms and factors which are implicated in Müller cell-mediated neuroprotection, immunomodulation, regulation of Müller cell proliferation, upregulation of intermediate filaments, glial scar formation, and the generation of neural progenitor/stem cells. A proper understanding of the signaling mechanisms implicated in gliotic alterations of Müller cells is essential for the development of efficient therapeutic strategies that increase the supportive/protective and decrease the destructive roles of gliosis.

Mapping of the neonatal Fc receptor in the rodent eye

PURPOSE

The neonatal Fc receptor (FcRn) has been known to modulate IgG transport and protect against IgG catabolism, resulting in extension of the serum half-life of IgG. The goal of this study was to localize FcRn receptor expression in the rat's eye.

METHODS

The cornea, retina, conjunctiva, ciliary body and iris, retinal pigment epithelium and choroid, and lens were dissected from each rat's eye, and total RNA was purified. The first-strand cDNAs were synthesized and subjected to PCR reaction. For control samples, reverse transcriptase was omitted. A monoclonal antibody against the FcRn heavy chain was used to localize the distribution of the FcRn receptor in ocular tissues. Lymphatic vessels and blood vessels were stained with a rabbit anti-mouse lymphatic vessel endothelial receptor-1 polyclonal antibody and a rabbit anti-human von Willebrand factor polyclonal antibody, respectively.

RESULTS

RT-PCR demonstrated expression of FcRn RNA in cornea, retina, conjunctiva, ciliary body and iris, and lens but absence of expression in the retinal pigment epithelium and choroid. Immunohistochemistry and double staining confirmed the expression of FcRn receptor to the conjunctival lymphatic vessels but not in the conjunctival blood vessels. In the ciliary body, the FcRn receptor was found to be expressed in both the nonpigmented ciliary epithelium and the ciliary blood vessels. The expression of FcRn receptor was confirmed in the retinal blood vessels, iris blood vessels, optic nerve vascular structures, corneal epithelium and endothelium, and lens epithelium.

CONCLUSIONS

The FcRn receptor is expressed in multiple ocular tissues. The blood-ocular barrier showed FcRn receptor expression, indicating that IgG transport from ocular tissues to the blood system may use this receptor. The role of the FcRn receptor in the anterior segment and the conjunctiva remains unclear.