Immunopathology of reactivation of experimental ocular histoplasmosis.

We have established a non-human primate model of experimental ocular histoplasmosis. This model has been shown to result in chronic lesions that resemble typical 'histo spots' or choroidal scars but that contain infiltrates of lymphocytes for as long as 10 yr following intracarotid injection of live Histoplasma capsulatum. Using this model, we attempted to reactive these late choroidal lesions via intracarotid challenge with specific antigen (heat-killed H. capsulatum). No clinical changes suggestive of reactivation of these lesions were observed following this antigenic challenge. However, immunopathologic analysis of choroidal lesions at 1, 3 and 7 days after antigenic challenge revealed significant increases in both the numbers of inflammatory cells and the relative percentages of the helper/inducer lymphocyte and macrophage populations. Our results demonstrate that, following antigenic challenge, a cellular change, consistent with a type IV delayed hypersensitivity, can be observed in previously active, but clinically quiescent, histoplasmosis lesions. In light of the many parallels between our primate experimental model and human ocular histoplasmosis, our findings suggest that, in the human, significant immunopathologic activity may occur subclinically in the choroid of affected individuals. It is possible that repeated bouts of subclinical reactivation may induce or enhance chronic choroiditis and, over many years, ultimately produce slow progressive damage to the Bruch's membrane/retinal pigment epithelium complex, resulting in clinically 'active' macular disease and, in selected cases, subretinal neovascularization.

Immunopathology of chronic experimental histoplasmic choroiditis in the primate.

A nonhuman primate model of ocular histoplasmosis was developed that enabled the authors to define the choroidal cellular immunopathology of both the acute and chronic phases of experimental histoplasmic choroiditis. Anti-human monoclonal antibodies were used to identify the inflammatory cell subsets and to calculate their relative percentages in the choroidal inflammatory lesions. Comparison of the acute (less than or equal to 65 days) and chronic (greater than or equal to 1 yr) phases suggested possible variations in the evolution of these lesions, resulting in the development of immunopathologically distinct chronic lesions. In this model, these late lesions could be differentiated by the presence or absence of dense lymphocytic foci, comprised predominantly of mature B-lymphocytes, located within the more diffuse inflammatory cell background. The chronic lesions containing these B-cell foci had significantly higher percentages of both mature B-cells (P less than 0.0001) and helper-inducer T-cells (P less than 0.05) than did the chronic lesions without B-cell foci. The increase in helper-inducer T-cells in the chronic lesions with B-cell foci resulted in a higher mean helper-suppressor T-cell ratio (mu = 0.60) than that seen in lesions lacking foci (mu = 0.33). These findings suggest that, even in the same eye, individual chronic histoplasmic choroidal lesions, which clinically resemble "histo spots" in humans, may have different immunopotentials.

Meibomian gland dysfunction. II. The role of keratinization in a rabbit model of MGD.

Meibomian gland dysfunction (MGD) was induced in 34 albino rabbits by the twice-daily topical application of 2% epinephrine over a period of 6 months to 1 year. Seven age-matched control rabbits, not receiving epinephrine, were followed up for a similar period. All lids were evaluated pre- and post-treatment by gross clinical examination and by transillumination biomicroscopy and photography. Of the 68 rabbit lids evaluated, 56% developed signs of MGD, which ranged from plugging of the meibomian gland orifice and presence of microcysts (subclinical lesions; 30.9% of the lids) to opacification and enlargement of the glands with increasing severity (clinical lesions; 25.0% of the lids). The remaining lids (44%) remained normal. MGD did not develop in the seven control rabbits. After the development of MGD, lids were evaluated by immunofluorescent microscopy, SDS-PAGE and Western blotting using mouse monoclonal antibodies to keratin proteins. Development and progression of MGD in the rabbit appears to correlate with increasing stratification and keratinization of the meibomian gland duct epithelium. In the early stages of MGD, focal areas of epithelial hyperkeratinization were identified by immunohistochemical staining using AE2 monoclonal antibody, specific for the 56.5 kD and 65-67 kD keratin protein marker for keratinized epidermis. As the severity of MGD progressed there was progressive increase in the AE2 staining of the duct epithelium. SDS-PAGE and immunoblotting of proteins from meibomian gland excreta in chronic MGD showed a progressive increase in both the 56.5 kD and 65-67 kD keratinization protein markers during development of MGD. We conclude that hyperkeratinization of the duct epithelium leading to plugging and dilation of the meibomian gland underlies the development of MGD following topical epinephrine treatment.