Anticomplement activity in human aqueous humor

Differential Effects of C1qa Ablation on Glaucomatous Damage in Two Sexes in DBA/2NNia Mice

PURPOSE

To determine the sex and age-related effects of C1qa ablation on retinal ganglion cell (RGC) and optic nerve (ON) axonal loss in a mouse model of glaucomatous neurodegeneration.

METHODS

Congenic C1qa mice were generated in the DBA/2NNia background. Female and male knockout (-/-), heterozygous (+/-), and wild type (+/+) mice were aged up to 14 months and IOPs were recorded in a subset of animals. Retinas of mice from all three groups at 5-6, 9-10 and 11-13 months of age were flat-mounted after retrograde labeling with Fluorogold. Imaged retinas were scored (RGC score) semi-quantitatively on a 10 point scale by two independent observers. A subset of retinas and optic nerves were also used for measurement of total number of RGCs. Semi-thin sections of ON were imaged and graded (ON score) for the amount of axonal damage semi-quantitatively, by two masked observers. Analysis of covariance (ANCOVA) was used for statistical comparisons. Microglial cells in flat-mounted retinas of 5-6 month old C1qa -/- and C1qa +/+ mice were used for assessment of microglial activation utilizing morphological criteria.

RESULTS

Female C1qa -/- mice had significantly higher IOP (p<0.000001, ANOVA) between 8 and 13 months of age compared to C1qa +/+ animals. No differences in IOPs between animals of the three genotypes were observed in males. At 5-6 months of age, there was no difference in RGC or ON scores between the three genotypes in animals of either sex. At 9-10 months of age, female mice didn't show significant differences in RGC or ON scores between the three genotypes. However, male C1qa -/- and C1qa +/- mice of the same age had better RGC and ON scores (p<0.003 and p<0.05, ANCOVA, for RGC and ON scores, respectively) compared with C1qa +/+ mice. At 11-13 months of age, female C1qa -/- mice had better RGC scores (p<0.006, ANCOVA) compared to C1qa +/+ and C1qa +/- animals. Accordingly, C1qa -/- mice had higher RGC counts (p<0.03, t-test) compared to C1qa +/+ animals. In male mice, there was a tendency for 12 month old C1qa -/- animals to have better RGC scores and higher RGC counts, but this didn't reach statistical significance. ON scores in 11-13 month old animals of either sex were not different between all three genotype. Microglial activation in male 5-6 month old C1qa -/- mice was decreased compared to C1qa +/+ animals; no such effect was seen in females.

CONCLUSIONS

Absence of C1qa ameliorates RGC and ON loss in the DBA/2NNia strain, but this effect differs between the two sexes. C1q-mediated RGC damage seems to be more potent than IOP-mediated RGC loss. In contrast, C1qa absence provides axonal protection early on, but this protection cannot overcome the effects of significant IOP elevation.

The potential of antibody-based immunosuppressive agents for corneal transplantation

Corneal transplantation is a sight-restorative procedure but its success is limited by irreversible graft rejection, which accounts for up to 50 per cent of failures. The normal eye is an immune-privileged site. Multiple mechanisms maintain ocular privilege, including the blood-eye barrier, the lack of blood vessels and lymphatics in the normal cornea, the relative paucity of mature antigen-presenting cells in the central cornea, the presence of immunomodulatory factors in ocular fluids, and the constitutive expressive of CD95L (Fas ligand) within the eye. However, privilege can be eroded by the sequelae of inflammation and neovascularization. Corneal graft rejection in humans is currently suppressed with topical glucocorticosteroids, which are moderately effective. Systemically administered immunosuppressive therapy is of limited efficacy and may be accompanied by unacceptable morbidity. Alternative therapies are needed to improve outcomes. Corneal graft rejection is primarily a cell-mediated response controlled by the CD4+ T cell, and thus CD4 and costimulatory molecule blockade are appealing targets for new therapeutic interventions. A number of monoclonal antibodies have shown promise as immunosuppressants to prolong corneal graft survival in experimental animal models, and may eventually prove to be useful adjuncts to corticosteroids.

Mechanisms of corneal graft rejection: the sixth annual Thygeson Lecture, presented at the Ocular Microbiology and Immunology Group meeting, October 21, 2000

The history of corneal transplantation reaches back over 150 years. Kissam performed one of the first penetrating keratoplasties when he transplanted a pig cornea onto a human in 1838. Only two interrupted sutures were used, and the surgery was performed without anesthesia! In retrospect, no one would be surprised to learn that the porcine corneal xenograft was rejected. Thirty years later, May transplanted rabbit corneal grafts to humans, but concluded that the failures in the first 24 attempts were the result of "imperfect technique and the inability to keep the eyes properly bandaged." The first documented report of a successful penetrating keratoplasty in a human subject was performed by Zirm in 1905. As we enter the new millennium, corneal transplantation remains the oldest, most common, and, arguably, the most successful form of solid tissue transplantation. In the United States alone, approximately 36,000 corneal transplants are performed each year. The success rate for corneal transplants is in excess of 90% in uncomplicated cases, even though HLA tissue typing is not performed and systemic immunosuppressive drugs are not administered. In spite of this extraordinary success, immune rejection remains the leading cause of corneal graft failure. Many inferences about the immunobiology of corneal graft rejection have been based on clinical observations; however, confirmation of these hypotheses requires prospective studies under controlled settings. The prudent use of animal models has fostered analytic studies on the immunobiology of corneal allografts without the complicating and confounding effects of topical steroids that are typically used on most keratoplasty patients. Although animal models of penetrating keratoplasty have been in use for almost a half-century, until recently, progress in understanding the immune mechanisms of corneal graft rejection has been slow. However, the widespread use of rodent models of orthotopic corneal transplantation has shed new light on the pathogenesis of corneal graft rejection.