Parisa Zamiri

Immunobiology and privilege of neuronal retina and pigment epithelium transplants.

Despite the existence of ocular immune privilege, immune rejection may be a barrier to successful retinal transplantation. We have examined in mice the extent to which the subretinal space (SRS) is an immune privileged site, and whether retinal pigment epithelium and neuronal retinal tissue have properties of immune privileged tissues. We report that (1) The SRS is an immune privileged site; (2) Neonatal RPE is an immune privileged tissue; (3) Neuronal retina is a partially immune privileged tissue; and (4) Microglia within neonatal neural retina grafts promote photoreceptor differentiation, become activated, and induce sensitization of the recipient and serve as targets of immune rejection.

Thrombospondin plays a vital role in the immune privilege of the eye

Purpose: The role of thrombospondin (TSP)-1 in TGF-β acti- vation and T-cell suppression was studied in the retinal pigment epithelial (RPE) cells, a monolayer of pigmented cells that line the subretinal space, an immune-privileged site in the eye. Methods: Posterior eyecups were prepared by excising the anterior segment, lens, and retina from enucleated eyes of C57BL/6, thrombospondin-1 knockout (TSP-1KO), and TGF-β2 receptor II double-negative (TGF-β 2R II DN) mice, leaving behind a healthy monolayer of RPE resting on choroid and sclera. Serum-free medium was added to these RPE eyecups, and, after various time intervals, supernatants (SNs) were removed and tested. Results: SN so fa ne xvivo culture of RPE cells from C57BL/6 mice were shown to inhibit both antigen and anti-CD3 activation of T cells, partially due to constitutive production of TGF-β and to the ability of RPE to activate the latent form of TGF-β .A ctivation of TGF-β was entirely dependent on TSP- 1, also produced by RPE. SNs of RPE from TSP-1KO mice failed to inhibit T-cell activation. Ovalbumin (OVA)-specific delayed hypersensitivity (DH) was not impaired when OVA was injected either into the subretinal space or into the anterior chamber of TSP-1KO mice before OVA immunization. Moreover, experimental autoimmune uveoretinitis was significantly more intense in eyes of TSP-1KO mice and failed to undergo spontaneous resolution unlike wild- type mice. Conclusions: Production of both TSP-1 and active TGF-β by RPE is essential to the creation and maintenance of immune privilege in the subretinal space and that the immune privilege limits the severity and duration of retinal inflammation due to autoimmunity.

Immunosuppressive properties of the pigmented epithelial cells and the subretinal space

The immune privilege of the anterior chamber of the eye has been recognized for over 100 years. However, the unique immunological properties of the pigmented epithelial (PE) cells of the eye and the subretinal space (SRS) have only recently been appreciated. The PE cells of the iris, ciliary body, and retina reside in anatomically disparate locations and serve distinctly different functions, yet share interesting immunomodulatory properties that contribute to ocular immune privilege. PE cells in the ciliary body and retina elaborate a variety of soluble factors that either directly or indirectly dampen immune-mediated inflammation; these include transforming growth factor-Beta, somatostatin, thrombospondin and pigment epithelial derived factor (PEDF). The constitutive expression of the immune co-stimulatory molecule, CD86, on iris PE cells not only inhibits T cell proliferation, but also promotes the generation of regulatory T cells. The SRS is now recognized as an immune-privileged site that shares many, but not all, of the properties ascribed to the anterior chamber, including the induction of systemic immune deviation. The prospect of therapeutic retinal transplantation and the possible immunologic etiology for some forms of age-related macular degeneration provides new impetus for gaining a better understanding of ocular immune privilege in the posterior regions of the eye.

Use of methotrexate in the management of sight-threatening uveitis

Managing chronic inflammatory immune-mediated eye diseases currently involves the non-specific suppression of the immune system. Oral corticosteroids are still the chief component of this therapy, but additional immunosuppressive agents are often indicated to control the disease as well as to avoid the side effects of long-term therapy with high doses of corticosteroids. Many different drugs are available including cyclosporine, azathioprine and occasionally cyclophosphamide, chlorambucil, or more recently mycophenolate mofetil and tacrolimus (FK-506). Pulsed low-dose oral methotrexate (MTX) is now widely used in rheumatological disease and has been introduced in the management of sight-threatening uveitis. Some reports using low doses advocate its use as an alternative when multiple drug therapy is necessary or to help lower the dose of other drugs. In our group of 11 patients with long-standing disease, adding MTX to the treatment regimen allowed control of the inflammation with a reduction of the corticosteroid dose in more than 50% of the cases and decreased the number of disease relapses in 45%. These results indicate that MTX is useful as an alternative option when a second/third agent is needed, achieving a better control of the disease in some cases.

G-CSF induces E-selectin ligand expression on human myeloid cells.

Clinical use of G-CSF can result in vascular and inflammatory complications. To investigate the molecular basis of these effects, we analyzed the adherence of G-CSF–mobilized human peripheral blood leukocytes (ML) to inflamed (TNF-α–stimulated) vascular endothelium. Studies using parallel plate assays under physiologic flow conditions and intravital microscopy in a mouse inflammation model each showed that ML take part in heightened adhesive interactions with endothelium compared to unmobilized (native) blood leukocytes, mediated by markedly increased E-selectin receptor-ligand interactions. Biochemical studies showed that ML express the potent E-selectin ligand HCELL (ref. 8) and another, previously unrecognized ∼65-kDa E-selectin ligand, and possess enhanced levels of transcripts encoding glycosyltransferases (ST3GalIV, FucT-IV and FucT-VII) conferring glycan modifications associated with E-selectin ligand activity. Enzymatic treatments and physiologic binding assays showed that HCELL and the ∼65-kDa E-selectin ligand contribute prominently to the observed G-CSF–induced myeloid cell adhesion to inflamed endothelium. Treatment of normal human bone marrow cells with a pharmacokinetically relevant concentration of G-CSF in vitro resulted in increased expression of these two molecules, coincident with increased transcripts encoding pertinent glycosyltransferases and heightened E-selectin binding. These findings provide direct evidence for a role of G-CSF in the induction of E-selectin ligands on myeloid cells, thus providing mechanistic insight into the pathobiology of G-CSF complications.

In vivo fluorescent imaging of the mouse retina using adaptive optics

In vivo imaging of the mouse retina using visible and near infrared wavelengths does not achieve diffraction-limited resolution due to wavefront aberrations induced by the eye. Considering the pupil size and axial dimension of the eye, it is expected that unaberrated imaging of the retina would have a transverse resolution of 2 microm. Higher-order aberrations in retinal imaging of human can be compensated for by using adaptive optics. We demonstrate an adaptive optics system for in vivo imaging of fluorescent structures in the retina of a mouse, using a microelectromechanical system membrane mirror and a Shack-Hartmann wavefront sensor that detects fluorescent wavefront.

IKKβ regulates essential functions of the vascular endothelium through kinase-dependent and -independent pathways

Vascular endothelium provides a selective barrier between the blood and tissues, participates in wound healing and angiogenesis, and regulates tissue recruitment of inflammatory cells. Nuclear factor (NF)-κB transcription factors are pivotal regulators of survival and inflammation, and have been suggested as potential therapeutic targets in cancer and inflammatory diseases. Here we show that mice lacking IKKβ, the primary kinase mediating NF-κB activation, are smaller than littermates and born at less than the expected Mendelian frequency in association with hypotrophic and hypovascular placentae. IKKβ-deleted endothelium manifests increased vascular permeability and reduced migration. Surprisingly, we find that these defects result from loss of kinase-independent effects of IKKβ on activation of the serine-threonine kinase, Akt. Together, these data demonstrate essential roles for IKKβ in regulating endothelial permeability and migration, as well as an unanticipated connection between IKKβ and Akt signalling.

Retinal progenitor cell xenografts to the pig retina: immunological reactions.

We evaluated the host response to murine retinal progenitor cells (RPCs) following transplantation to the subretinal space (SRS) of the pig. RPCs from GFP mice were transplanted subretinally in 18 nonimmunosuppressed normal or laser-treated pigs. Evaluation of the SRS was performed on hematoxylin-eosin (H&E)-stained sections. Serum samples were taken from naive and RPC-grafted pigs and mouse-reactive antibody responses were assessed. At 1 week, histology showed a few perivascular lymphocytes consistent with a mild retinal vasculitis, and depigmentation of the RPE with large numbers of mononuclear inflammatory cells in the choroid near the transplantation site. Large choroidal infiltrates were evident at 2–5 weeks. Serum from naive and RPC-xenografted pigs contained significant levels of preformed IgG and IgM antibodies against murine antigens. Xenogeneic RPCs transplanted to the porcine SRS induced mononuclear infiltration in the choroid with graft rejection occurring over 2–5 weeks. Serum analysis confirmed that mice and pigs are discordant species; however, a cell-mediated acute mechanism appears to be responsible, rather than an antibody-mediated rejection.

Imaging molecular expression on vascular endothelial cells by in vivo immunofluorescence microscopy.

Molecular expression on the vascular endothelium is critical in regulating the interaction of circulating cells with the blood vessel wall. Leukocytes as well as circulating cancer cells gain entry into tissue by interacting with adhesion molecules on the endothelial cells (EC). Molecular targets on the EC are increasingly being explored for tissue-specific delivery of therapeutic and imaging agents. Here we use in vivo immunofluorescence microscopy to visualize the endothelial molecular expression in the vasculature of live animals. High-resolution images are obtained by optical sectioning through the intact skin using in vivo confocal and multiphoton microscopy after in situ labeling of EC surface markers with fluorescent antibodies. Other vascular beds such as the bone marrow and ocular blood vessels can be imaged with little or no tissue manipulation. Live imaging is particularly useful for following the dynamic expression of inducible molecules such as E-selectin during an inflammatory response.

An adaptive optics biomicroscope for mouse retinal imaging

In studying retinal disease on a microscopic level, in vivo imaging has allowed researchers to track disease progression in a single animal over time without sacrificing large numbers of animals for statistical studies. Historically, a drawback of in vivo retinal imaging, when compared to ex vivo imaging, is decreased image resolution due to aberrations present in the mouse eye. Adaptive optics has successfully corrected phase aberrations introduced the eye in ophthalmic imaging in humans. We are using adaptive optics to correct for aberrations introduced by the mouse eye in hopes of achieving cellular resolution retinal images of mice in vivo. In addition to using a wavefront sensor to drive the adaptive optic element, we explore the using image data to correct for wavefront aberrations introduced by the mouse eye. Image data, in the form of the confocal detection pinhole intensity are used as the feedback mechanism to control the MEMS deformable mirror in the adaptive optics system. Correction for wavefront sensing and sensor-less adaptive optics systems are presented.