Anterior chamber-associated immune deviation: a review of the anatomical evidence for the afferent arm of this unusual experimental model of ocular immune responses

Post-Transplant Immune Tolerance in Rats Following Lymphocyte Injection Into the Anterior Chamber of the Eye

OBJECTIVE

We aimed to compare the clinical and histopathological results of skin graft transplants between rats that had been injected with lymphocytes into the anterior chamber of the eye with those that had not.

METHODS

A total of 16 Wistar albino, male rats were included in the study. Subjects were divided into 2 groups, namely a test group and a control group. Lymphocyte suspensions derived from the subjects of the control group were injected into the anterior chamber of the eye of each opposing subject of the test group. Also, an identical volume of physiological saline was injected into the anterior chamber of each subject in the control group to prevent bias. One week after this procedure, circular skin grafts of 1 cm in diameter were transplanted within the opposing groups. After a period of 1 week, transplanted graft tissues were excised to compare tissue healing.

RESULTS

The occurence of granulation and reepithelialization was more evident in the test group (96% and 33%, respectively, vs 80% and 17% for the control group, respectively). On the other hand, it was determined that acute inflammation was more intense in the control group (77% vs 50% for the test group).

CONCLUSION

We had created immune tolerance in rats through anterior chamber lymphocyte injection, which slowed down the rejection process. If this can be successfully implemented in practice, survival for transplant patients without long-term rejection will move closer to becoming a reality.

Matching for Human Leukocyte Antigens (HLA) in corneal transplantation - to do or not to do

As many patients with severe corneal disease are not even considered as candidates for a human graft due to their high risk of rejection, it is essential to find ways to reduce the chance of rejection. One of the options is proper matching of the cornea donor and recipient for the Human Leukocyte Antigens (HLA), a subject of much debate. Currently, patients receiving their first corneal allograft are hardly ever matched for HLA and even patients undergoing a regraft usually do not receive an HLA-matched graft. While anterior and posterior lamellar grafts are not immune to rejection, they are usually performed in low risk, non-vascularized cases. These are the cases in which the immune privilege due to the avascular status and active immune inhibition is still intact. Once broken due to infection, sensitization or trauma, rejection will occur. There is enough data to show that when proper DNA-based typing techniques are being used, even low risk perforating corneal transplantations benefit from matching for HLA Class I, and high risk cases from HLA Class I and probably Class II matching. Combining HLA class I and class II matching, or using the HLAMatchmaker could further improve the effect of HLA matching. However, new techniques could be applied to reduce the chance of rejection. Options are the local or systemic use of biologics, or gene therapy, aiming at preventing or suppressing immune responses. The goal of all these approaches should be to prevent a first rejection, as secondary grafts are usually at higher risk of complications including rejections than first grafts.

The Induction of Circulating, ACAID-Inducing Monocytes Requires CCR2/CCL2-Dependent Migration of Circulating F4/80(+) Cells into the Anterior Chamber

To determine the origin of peripheral blood mononulclear cells (PBMC) that activate regulatory T cells in anterior chamber-associated immune deviation (ACAID), fluorescein-labeled PBMC were intravenously injected into mice before the mice received an intracameral injection of antigen. Six-24 hr after intracameral injection, fluorescein-labeled PBMC increased in the iris. Twenty-four-48 hr labeled cells decreased in the iris and increased in the thymus and spleen. The entry of the labeled PBMC into the anterior chamber and subsequent production of PBMC that transfer ACAID required the expression of CCR2 by the PBMC and the production of the chemokine CCL2 by the recipient of the PBMC. The results suggest that the intracameral injection of antigen induces i) the infiltration of F4/80⁺ PBMC into the AC, ii) where these PBMC are converted to a regulatory phenotype, and iii) recirculate to activate T cells that suppress cell-mediated immunity.

Absence of systemic immune response to adenovectors after intraocular administration to children with retinoblastoma

The ocular environment has been shown to induce tolerance to locally administered antigens. We therefore investigated whether there was a systemic immune response against adenoviral vectors injected into the vitreous of retinoblastoma patients enrolled in a phase 1 clinical trial of adenoviral-mediated thymidine kinase gene transfer. Sections of enucleated eyes were immunostained with antibodies against inflammatory cells. A trend toward increasing numbers of plasma cells, T cells, macrophages, and antigen-presenting cells was observed in the injected subjects' eyes, but systemically, there was no significant increase in the number of adenovirus-specific cytotoxic T lymphocytes (CTLs) or in adenovirus neutralizing antibodies. Therefore, in contrast to studies showing significant immunogenicity of Ad-RSVtk following injection into extraocular tumors, injection into the eye produces only a mild local inflammatory response without evidence of systemic cellular or humoral immune responses to adenovirus.

Immune privilege of corneal allografts

Corneal transplantation has been performed successfully for over 100 years. Normally, HLA typing and systemic immunosuppressive drugs are not utilized, yet 90% of corneal allografts survive. In rodents, corneal allografts representing maximal histoincompatibility enjoy >50% survival even without immunosuppressive drugs. By contrast, other categories of transplants are invariably rejected in such donor/host combinations. The acceptance of corneal allografts compared to other categories of allografts is called immune privilege. The cornea expresses factors that contribute to immune privilege by preventing the induction and expression of immune responses to histocompatibility antigens on the corneal allograft. Among these are soluble and cell membrane molecules that block immune effector elements and also apoptosis of T lymphocytes. However, some conditions rob the corneal allograft of its immune privilege and promote rejection, which remains the leading cause of corneal allograft failure. Recent studies have examined new strategies for restoring immune privilege to such high-risk hosts.

Subretinal delivery of adeno-associated virus serotype 2 results in minimal immune responses that allow repeat vector administration in immunocompetent mice

Background

Adeno-associated virus serotype 2 (AAV2) vectors show considerable promise for ocular gene transfer. However, one potential barrier to efficacious long-term therapy is the development of immune responses against the vector or transgene product.

Methods

We evaluated cellular and humoural responses in mice following both single and repeated subretinal administration of AAV2, and examined their effects on RPE65 and green fluorescent protein transgene expression.

Results

Following subretinal administration of vector, splenocytes and T-cells from draining lymph nodes showed minimal activation following stimulation by co-culture with AAV2. Neutralizing antibodies (NAbs) were not detected in the ocular fluids of any mice receiving AAV2 or in the serum of mice receiving a lower dose. NAbs were present in the serum of a proportion of mice receiving a higher dose of the vector. Furthermore, no differences in immunoglobulin titre in serum or ocular fluids against RPE65 protein or AAV2 capsid between treated and control mice were detected. Histological examination showed no evidence of retinal toxicity or leukocyte infiltration compared to uninjected eyes. Repeat administration of low-dose AAV.hRPE65.hRPE65 to both eyes of RPE65^−/− mice resulted in transgene expression and functional rescue, but re-administration of high-dose AAV2 resulted in boosted NAb titres and variable transgene expression in the second injected eye.

Conclusions

These data, which were obtained in mice, suggest that, following subretinal injection, immune responses to AAV2 are dose-dependent. Low-dose AAV2 is well tolerated in the eye, with minimal immune responses, and transgene expression after repeat administration of vector is achievable. Higher doses lead to the expression of NAbs that reduce the efficacy of repeated vector administration. Copyright © 2009 John Wiley & Sons, Ltd.

Typisierung beim HLA-Matching

Matching of human leukocyte antigens of donors and recipients (HLA matching) plays a significant role in kidney, heart, lung, and stem cell transplantation. New data demonstrate that HLA matching also significantly prolongs the survival of corneal grafts. The reasons for the late recognition of the significance of HLA matching in corneal transplantation are on the one hand the immune privilege of the eye, which allows corneal transplantation under certain conditions without immunosuppressive therapy, and on the other hand highly erroneous serological typing. Recent molecular DNA typing is almost without errors, and the selection of grafts on the basis of results obtained using this method will improve the long-time survival of future corneal grafts. Today, there are several reasons arguing for the general practice of HLA matching in keratoplasty.

Matching of the minor histocompatibility antigen HLA-A1/H-Y may improve prognosis in corneal transplantation

BACKGROUND

Minor histocompatibility (H) antigens are peptides of allelic intracellular proteins that play an important role in human leukocyte antigen (HLA) matched transplantations. In an animal model of keratoplasty, minor H antigens have even been reported to exceed the immunogenicity of major H antigens (MHC). This investigation is to assess any benefit of matching the broadly expressed gender (H-Y) and HA-3 antigens in HLA-A1 donor positive human keratoplasty.

METHODS

A total of 229 HLA-A1 donor positive keratoplasties were analyzed. A Cox proportional hazards model and Kaplan-Meier analysis were applied to estimate the effect of H-Y or HA-3 mismatches on rejection-free graft survival.

RESULTS

Eighty-one cases were mismatched for H-Y (male donor to female recipient). A mean follow up of two years showed graft survival as high as 88% in the H-Y compatible group compared to only 77% in the H-Y mismatched group (P = 0.02). Eight out of 62 cases were mismatched for HA-3. No statistically significant influence of HA-3 matching on rejection-free graft survival was observed (85% vs. 73%, P=0.52).

CONCLUSION

HLA-A1/H-Y matching and matching for other broadly expressed minor H antigens may further improve prognosis in keratoplasty.

New insights into the cell biology of the marginal zone of the spleen

In the marginal zone of the spleen the bloodstream passes through an open system of reticular cells and fibers in which various myeloid and lymphoid cells are located. Macrophages in this region are well equipped to recognize pathogens and filter the blood by virtue of unique combinations of pattern recognition receptors. They interact with a specific set of B cells that can be found only in the marginal zone and that are able to react rapidly to bacterial antigens in particular. This combination of strategically located cells is an important factor in our defense against blood-borne pathogens. New data on the development of the marginal zone itself and the marginal zone B cells are reviewed and discussed in light of the function of the spleen in host defense.