Acanthamoeba keratitis: a clinicopathologic case report and review of the literature.

The immune response elicited by corneal Acanthamoeba infection remains incompletely understood. The infected cornea removed from a patient with Acanthamoeba keratitis during therapeutic penetrating keratoplasty was analyzed by immunohistochemistry. Heavy infiltration of neutrophils and, to a lesser extent, macrophages was observed throughout the cornea with both cell types in direct apposition to Acanthamoeba parasites. While T and B cells were identified in the corneal stroma, none were seen in direct proximity to Acanthamoeba parasites. Natural killer (NK) cells were absent from the cornea. These results demonstrate that neutrophils and macrophages of the innate immune system predominate in the host response against Acanthamoeba infection of the human cornea, confirming the relevance of animal models of Acanthamoeba keratitis that recapitulate these findings. Lymphocytes appear to be excluded from regions of the cornea containing Acanthamoeba parasites, despite the presence of a corneal lymphocytic response in this case, suggesting inhibition of lymphocyte chemotaxis toward the parasite.