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.