Recrudescence is a common and troubling feature of Acanthamoeba keratitis and suggests that corneal infection with this organism fails to stimulate the systemic immune apparatus. The present study examined the cell-mediated and humoral immune responses to Acanthamoeba keratitis in the Chinese hamster. Corneal infection with A. castellanii failed to induce either delayed-type hypersensitivity (DTH) or serum IgG antibody against parasite antigens. The failure to induce cell-mediated and humoral immunity did not result in anergy or tolerance since subsequent intramuscular (i.m.) immunization with parasite antigens elicited robust DTH and IgG antibody responses. The inability of corneal infections to induce primary cell-mediated immune responses was due to the absence of resident antigen-presenting cells in the central cornea because induction of Langerhans cell (LC) migration into the central cornea prior to infection with Acanthamoeba promoted the development of parasite-specific DTH. Although the presence of resident LC did not promote the development of a primary humoral immune response, subsequent i.m. immunization elicited heightened parasite-specific IgG antibody production which was indicative of an anamnestic response. Collectively, the results indicate that in the absence of resident antigen-presenting cells, corneal infection with Acanthamoeba fails to stimulate primary cell-mediated or humoral immunity. Induction of peripheral LC into the central corneal epithelium promotes the development of parasite-specific DTH, but does not exacerbate corneal disease.

Acanthamoeba castellanii, one isolate from the eye and one from the soil, were compared on the basis of: (a) pathogenic potential; (b) plasminogen activator activity; (c) chemotactic activity; (d) cytopathic effects; (e) collagenolytic activity; (f) binding ability to contact lenses; and (g) and binding ability to corneal buttons. The ocular isolate of A. castellanii was found to be pathogenic based on its ability to produce corneal infections in Chinese hamsters. By contrast, the soil isolate produced only mild lesions in a single Chinese hamster. Amoebae from the ocular isolate bound to corneal epithelium in greater numbers than the soil isolate counterparts. Moreover, ocular isolate organisms displayed plasminogen activator activity that was not detected in cultures from soil isolates of A. castellanii. Although neither the soil isolate nor the ocular isolate amoebae responded chemotactically to epithelial or stromal components, the ocular isolate displayed a curious and reproducible positive chemotactic response to endothelial extracts. Both A. castellanii isolates produced cytopathic effects on pig corneal epithelium, however the cytotoxicity from the ocular isolate was significantly greater than that of the soil isolate. The results indicate that the pathogenic potential of A. castellanii is correlated with the parasite's capacity to bind to corneal epithelium, respond chemotactically to corneal endothelial extracts, elaborate plasminogen activators, and produce cytopathic effects on corneal epithelium.

A follow-up study of 113 patients with suspicious iris nevi who were referred to our clinic between 1973 and 1991 was carried out by: reviewing their clinical records, fluorescein angiography, obtaining recent data with cooperation of their own or the referring ophthalmologist and contacting patients for reexamination. After examination the diagnoses were: 64 suspicious nevi, 23 melanomas, 15 ciliary body tumors with iris involvement and 11 other pseudomelanomas. In the group of suspicious nevi 86% was localized in the inferior part and 66% in the temporal part of the iris; for the melanoma group these figures were 78% and 75% respectively. The chamber angle was more often involved in the melanoma group, 40% against 17% in the suspicious nevi group. In this group 11 cases (21.6%) showed growth during the follow-up (mean 10.6 years). In three cases the tumor was surgically removed, with as histopathologic diagnosis: 1 xanthogranuloma, 1 neurolemmoma and 1 possible melanoma. In the melanoma group 16 lesions (76%) showed growth during the follow-up (mean 7.2 years), in most cases within 5 years of the initial diagnosis. The lesion was surgically removed in 11 cases. The histopathologic diagnoses were: 8 melanomas, 1 xanthogranuloma, 1 possible melanoma and 1 metastasis of a skin melanoma. Our study shows that periodic ophthalmic check-ups are of great importance in the management of iris lesions suspect for melanoma.

Interferon-alpha can be used as additional treatment of herpes keratitis. However, several studies have demonstrated that interferon-alpha can induce immunological changes in several tissues, and if used in a patient with a corneal transplantation, those changes might induce rejection of the corneal transplant. In order to determine the immunological changes in corneal tissue, we examined the effect of local treatment with interferon-alpha on MHC Class I and II expression, and inflammatory cell influx in the rat eye, and compared this with the changes induced by intrastromal sutures. These changes were evaluated by immunohistology for MHC Class I and II and several immunologically active cells. Intrastromal sutures induced an influx of lymphocytes and macrophages and induction and/or upregulation of MHC Class I and II. Local treatment with interferon-alpha did not have any of these effects. We conclude that topical use of interferon-alpha is not likely to induce rejection of a corneal graft.