Person:

Chauhan, Sunil

Purpose: Anterior chamber associated immune deviation (ACAID) is an antigen-specific form of peripheral immune tolerance that is induced to exogenous antigens placed in the ocular anterior chamber, which leads to a suppression in delayed-type hypersensitivity (DTH). Considerable work has been done on ACAID induction to major histocompatibility (MHC) alloantigens. However, its role on cytotoxic T lymphocyte (CTL) activity is currently unknown. Methods: C57BL/6 (H-2b) mice received an intracameral (IC) inoculation with BALB/c (H-2d) splenocytes. Splenic CD4+ and CD8+ T cell populations were characterized by flow cytometry and proliferation assays during induction and expression phases of ACAID. Percentages of CD4+CD25+FoxP3+ T regulatory cells (Treg) were also followed. Lastly, CTL function was measured at various time points during ACAID expression, and Treg were added to identify potential alterations in CTL function. Results: CD4+ and CD8+ T cell percentages and proliferation increased in the spleen during ACAID induction but then sharply decreased in response to an allospecific immunization. Expression of ACAID also exhibited a significant drop in CTL function. However, while Treg expansion was observed, these cells did not directly mediate the CTL inhibition. Conclusions: ACAID mediates an inhibition of CTL function against MHC alloantigens. Furthermore, we found that ACAID induction leads to the expansion and proliferation of CD4+ and CD8+ T cells while ACAID expression is associated with a diminishment in T cell percentages due to proliferation impairment. Lastly, Treg also expand during ACAID induction. However, our data suggest that Treg do not directly inhibit CTL activity.

The normal cornea is devoid of lymphatic and blood vessels, thus suppressing both the afferent (lymphatic) and efferent (vascular) arms of the immune response–contributing to its ‘immune privilege’. Inflammation, however, negates this unique ‘immune’ and ‘angiogenic’ privilege of the cornea. Abnormal blood vessel growth from pre-existing limbal vessels into the cornea has been studied for many years, but it is only recently that the significance of new lymphatic vessels (lymphangiogenesis) in ocular inflammatory diseases has been demonstrated. Whereas blood vessels in inflamed ocular surface provide a route of entry for immune effector cells to the cornea, lymphatics facilitate the exit of antigen-presenting cells and antigenic material from the cornea to regional lymph nodes, thus promoting induction of adaptive immune response. This review summarizes the current evidence for lymphangiogenesis in the cornea, and describes its molecular mediators; and discusses the interface between corneal lymphangiogenesis and adaptive immunity. Furthermore, the pathophysiologic implications of corneal lymphangiogenesis in the setting of allo- and autoimmune-mediated corneal inflammation are discussed.

Purpose To identify the role of chemokine receptor 6 (D6) expression by dendritic cells (DCs) and its role in corneal transplant immunity. Methods: Flow cytometry analysis was used to assess the expression level of the D6 chemokine receptor in different leukocyte populations and DC maturation following lipopolysaccharides (LPS) stimulation of bone marrow–derived DCs isolated from wild-type (WT) or D6−/− mice (C57BL/6 background). Mixed-lymphocyte reactions and delayed-type hypersensitivity assays were performed with bone marrow–derived DCs from WT or D6−/− mice to evaluate T-cell alloreactivity. Adoptive transfer experiments with T cells from WT or D6−/− hosts with BALB/c corneal allografts were performed. Graft opacity was assessed over an 8-week period, and graft survival was plotted using Kaplan–Meier survival curves. Results: Expression of the D6 chemokine receptor was significantly higher in DCs compared to other leukocyte subpopulations, including neutrophils, lymphocytes, and monocytes/macrophages. LPS challenge of D6−/− bone marrow–derived DCs elicited significantly lower levels of major histocompatibility complex II and costimulatory molecules (CD40, CD80, and CD86) compared to WT bone marrow–derived DCs, indicating the role of the D6 chemokine receptor in DC maturation. Further, DCs isolated from D6−/− mice induced less T-cell proliferation (p≤0.001) and interferon-gamma production in T cells of draining lymph nodes compared to WT mice following corneal transplantation (p≤0.001). Moreover, adoptively transferred T cells from D6−/− corneal transplanted mice to WT mice led to impaired graft rejection, compared to the hosts that received T cells from the WT transplanted mice. Conclusions: We demonstrated D6 chemokine receptor expression by DCs and identified its critical function in multiple aspects of DC biology, including maturation and consequent elicitation of alloreactive T-cell responses that are responsible for corneal allograft rejection.

Recent experimental and clinical data suggest that there is a link between dry eye disease (DED) and T cell-mediated immunity. However, whether these immune responses are a consequence or cause of ocular surface inflammation remains to be determined. Thus far, only models of acute DED have been used to derive experimental data. This is in contrast to clinical DED which usually presents as a chronic disease. In the present study, using a murine model of chronic DED, it was established that the chronic phase of the disease is accompanied by Th17 responses at the ocular surface, and that a significant memory T cell population can be recovered from chronic DED. This memory response is predominantly mediated by Th17 cells. Moreover, adoptive transfer of this memory T cell population was shown to induce more severe and rapidly progressing DED than did the adoptive transfer of its effector or naïve counterparts. Not only do these results clearly demonstrate that effector memory Th17 cells are primarily responsible for maintaining the chronic and relapsing course of DED, but they also highlight a potentially novel therapeutic strategy for targeting memory immune responses in patients with DED.

The tear film, lacrimal glands, corneal and conjunctival epithelia and Meibomian glands work together as a lacrimal functional unit (LFU) to preserve the integrity and function of the ocular surface. The integrity of this unit is necessary for the health and normal function of the eye and visual system. Nervous connections and systemic hormones are well known factors that maintain the homeostasis of the ocular surface. They control the response to internal and external stimuli. Our and others’ studies show that immunological mechanisms also play a pivotal role in regulating the ocular surface environment. Our studies demonstrate how anti-inflammatory factors such as the expression of vascular endothelial growth factor receptor-3 (VEGFR-3) in corneal cells, immature corneal resident antigen-presenting cells, and regulatory T cells play an active role in protecting the ocular surface.

Dry eye disease (DED) affects millions of people worldwide and negatively influences the quality of life for patients. In its most severe forms, DED may lead to blindness. The etiology and pathogenesis of DED remain largely unclear. Nonetheless, in this review we summarize the role of the disruption of afferent and efferent immunoregulatory mechanisms that are responsible for the chronicity of the disease, its symptoms, and its clinical signs. We illustrate current anti-inflammatory treatments for DED and propose that prevention of the disruption of immunoregulatory mechanisms may represent a promising therapeutic strategy towards controlling ocular surface inflammation.

Foxp3 expressing CD4+CD25+ regulatory T cells (Tregs) have been shown to prevent allograft rejection in clinical and animal models of transplantation. However, the role of Foxp3 in regulating Treg function, and the kinetics and mechanism of action of Tregs in inducing allograft tolerance in transplantation, are still not fully understood. Thus, we investigated the kinetics and function of Tregs in a mouse model of orthotopic corneal transplantation, the most common form of tissue grafting worldwide. Here using in-vitro functional assays and in-vivo Treg adoptive transfer assays, we show that far more relevant than Treg frequency is their level of Foxp3 expression, which is directly associated with the potential of Tregs to prevent allograft rejection by producing regulatory cytokines and suppressing effector T cell activation. In addition, our data clearly demonstrate that Tregs primarily suppress the induction of alloimmunity in regional draining lymph nodes, rather than suppressing the effector phase of the immune response in the periphery. These findings provide new insights on Treg dynamics in transplantation which are crucial for designing therapeutic strategies to modulate Treg function, and to optimize Treg-based cell therapies for clinical translation.

Certain components of a graft that provoke alloimmunity may not be vital for graft function or critical as targets of rejection. Corneal transplantation is an example of this since graft epithelium plays a role in allosensitization, while corneal graft endothelium—which shares the same alloantigens—is the critical target in allorejection. In this study, we found that exploiting this biology by replacing donor epithelium of an allograft with an allodisparate 3rd-party epithelium yields a marked enhancement in transplant survival. Such “chimeric” allografts consisted of a C3H/He (H-2k) corneal epithelium over a C57BL/6 (H-2b) epithelial-denuded cornea (or v.v.) and orthotopically placed on BALB/c (H-2d) hosts. Conventional corneal allografts (C3H/He, or C57BL/6) or isografts (BALB/c) were also transplanted on BALB/c hosts. Alloreactive T cell frequencies (CD4+ IFN-gamma+) primed to graft endothelium were strongly diminished in chimeric relative to conventionally allografted hosts. This was corroborated by decreased T cell infiltration (p=0.03) and a marked enhancement of allograft survival (p=0.001). Our results represent the first successful demonstration of chimeric tissue, epithelial-denuded allograft plus 3rd-party allodisparate epithelium, in the promotion of allograft survival. Moreover, chimeric grafting can be readily performed clinically, whereby corneal allograft rejection remains a significant problem particularly in inflamed graft beds.

purpose. Dry eye disease (DED) is associated with ocular surface inflammation that is thought to be mediated primarily by CD4 T cells. The purpose of this study was to investigate whether this T cell–mediated immune response is generated in the lymphoid compartment and to characterize the functional phenotype of the T cells activated in DED.

methods. DED was induced in female C57BL/6 mice by exposure to a desiccating environment in the controlled environment chamber and to systemic scopolamine. T cells from regional draining lymph nodes (LNs) of DED mice and normally sighted mice were analyzed for surface activation markers (CD69 and CD154), chemokine and cytokine receptors, and proliferation potential.

results. Draining LNs of DED mice showed increased frequencies of CD69- and CD154-expressing T cells with higher proliferative capacity. In addition, these LN T cells primarily showed a helper T-cell (Th)1 phenotype, expressing significantly higher levels of IFN-γ and IL-12Rβ2 but not IL-4R. Similarly, the LNs of DED mice showed significantly increased frequencies of T cells expressing CXCR3 and CCR5, but not CCR4, suggesting a bias toward a Th1 phenotype.

conclusions. These data demonstrate that a Th1-type immune response is induced in the regional LNs of DED mice. The identification of specific cytokine/chemokine receptors overexpressed by these T cells may signify potential novel targets/strategies for the treatment of DED.

Purpose

In the present study, the authors developed novel models to stimulate blood vessel formation (hemangiogenesis) versus lymphatic vessel formation (lymphangiogenesis) in the cornea.

Methods

Micropellets loaded with high-dose (80 ng) or low-dose (12.5 ng) basic fibroblast growth factor (bFGF) were placed in BALB/c corneas. Angiogenic responses were analyzed by immunohistochemistry to quantify blood neovessels (BVs) and lymphatic neovessels (LVs) to 3 weeks after implantation. Areas covered by BV and LV were calculated and expressed as a percentage of the total corneal area (percentage BV and percentage LV). Hemangiogenesis (HA) and lymphangiogenesis (LA) were also assessed after antibody blockade of VEGFR-2 or VEGFR-3

Results

Although high-dose bFGF stimulation induced a more potent angiogenic response, the relative LV (RLV = percentage LV/percentage BV × 100) was nearly identical with high- and low-doses of bFGF. Delayed LA responses induced 3 weeks after implantation of high-dose bFGF resulted in a lymphatic vessel-dominant phenotype. Interestingly, the blockade of VEGFR-2 significantly suppressed BV and LV. However, the blockade of VEGFR-3 inhibited only LV (P = 0.0002) without concurrent inhibition of BV (P = 0.79), thereby resulting in a blood vessel-dominant phenotype

Conclusions

An HA-dominant corneal phenotype can be obtained in BALB/c mice 2 weeks after implantation of an 80-ng bFGF micropellet with VEGFR-3 blockade. Alternatively, an LA-dominant corneal phenotype can be obtained 3 weeks after implantation of an 80-ng bFGF micropellet without supplementary modulating agents. These models will be useful in evaluating the differential contribution of BV and LV to a variety of corneal abnormalities, including transplant rejection, wound healing and microbial keratitis.

Dry eye disease (DED), an inflammatory autoimmune disorder affecting the ocular surface, degrades visual performance and the quality of life of more than 10 million people in the United States alone. The primary limitation in the effective treatment of DED is an incomplete understanding of its specific cellular and molecular pathogenic elements. Using a validated mouse model of DED, herein we functionally characterize the different T cell subsets, including regulatory T cells (Tregs) and pathogenic effector T cells, and determine their contribution to the pathogenesis of DED. Our data demonstrate the presence of dysfunctional Tregs and the resistance of pathogenic T cells, particularly Th17 cells, to Treg suppression in DED. In addition, we clearly show that in vivo blockade of IL-17 significantly reduces the severity and progression of disease, which is paralleled by a reduction in the expansion of Th17 cells and restoration of Treg function. Our findings elucidate involvement of a previously unknown pathogenic T cell subset (Th17) in DED which is associated specifically with Treg dysfunction and disease pathogenesis, and suggest a new target for dry eye therapy.