A new morphologic manifestation of Langerhans cells in guinea pig corneal transplants

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.

ATPase-positive dendritic cells in the limbal and corneal epithelium of guinea pigs after extended wear of hydrogel lenses

PURPOSE

It has been said that Langerhans cells can be induced to migrate into the central cornea by various stimuli. We investigated whether extended wear of hydrogel lenses induced the migration of Langerhans cells into the central cornea.

METHODS

Guinea-pig eyes were fitted with hydrogel contact lenses, and the number of adenosine triphosphatase (ATPase)-positive dendritic cells at the limbus, peripheral, and central corneal epithelium was quantified after 1, 2, 4, and 8 nights of extended wear. The cells were identified with histochemical procedures using ATPase stain.

RESULTS

At baseline, ATPase-positive dendritic cells were seen at the limbus and peripheral cornea, with the density decreasing from limbus to peripheral cornea. There were no cells in the central cornea. With extended wear, cells increased in number at the peripheral cornea from 2 nights onward, and cells were seen in the central cornea from 4 nights onward.

CONCLUSION

Extended wear of hydrogel lenses induced migration of ATPase-positive dendritic cells (Langerhans cells) into the central cornea. It is possible that they may play a role in the pathophysiology of some of the adverse events seen with contact lens wear.

Effect of cytokine-induced migration of Langerhans cells on corneal allograft survival

The unique paucity of Ia+ Langerhans cells (LCs) in the central cornea contributes to the immunological privilege of corneal allografts. A variety of stimuli can induce the centripetal migration of peripheral LCs. At least one of these stimuli (i.e. latex bead instillation) induces interleukin-1 (IL-1) secretion by corneal cells which acts as a potent chemoattractant for LCs. Within 30 minutes of intracorneal injection of IL-1, centripetal migration of LCs can be detected. The presence of donor-derived LCs in corneal allografts doubles the incidence of rejection of fully allogeneic corneal allografts as well as MHC matched, multiple minor H mismatched corneal allografts. Although the presence of donor-specific LCs greatly jeopardises corneal allograft survival, migration of host-derived LCs into corneal allografts does not appear to increase the risk of rejection.

Regulators of immunological responses in the cornea and the anterior chamber of the eye

Although the eye is considered to be immunologically privileged, this privilege is not absolute. This is well demonstrated by, for example, the fate of corneal transplantations. Clinical studies in man and experimental studies in animals have shown that survival of a corneal transplant depends on the local condition of the cornea and the anterior chamber of the eye. The presence of neovascularisation or Langerhans cells in the recipient cornea endangers the graft, while the intracorneal production of immunosuppressive factors may inhibit the development of rejection. The balance between suppressive and stimulatory factors determines whether a local immune response will develop.

The role of the limbus in corneal allograft rejection

The state of the recipient peripheral cornea and limbus exerts a strong influence on subsequent corneal graft survival. In particular, graft outcome is influenced by the number of dendritic cells (Langerhans cells) that have infiltrated the graft bed from the limbus. The number of dendritic cells present in the donor button also affects subsequent graft survival.

Leukocytes in the graft bed associated with corneal graft failure. Analysis by immunohistology and actuarial graft survival

Immunohistochemical staining analysis using monoclonal antibodies was performed on 107 recipient corneas removed at graft. There were significantly more infiltrating cells bearing one or more of the leukocyte-common antigen, class II major histocompatibility complex antigens, various myeloid-lineage markers, and a peripheral T cell marker, in the graft beds of those recipients who subsequently lost a corneal graft than there were in the graft beds of those for whom the outcome was successful. The hypothesis that large numbers of leukocytes in the recipient graft bed would be correlated with subsequent graft failure was examined by actuarial graft survival analysis. Recipients whose corneas contained fewer than 50 leukocyte-common antigen-positive cells/mm2 of corneal stroma showed a 3-year actuarial graft survival of 83%, compared with 39% in those whose corneas contained more than 50 such cells/mm2. The corneal leukocyte count was a particularly useful prognostic indicator of outcome in those patients judged clinically to be at risk of graft failure.