Effect of human tears on Acanthamoeba-induced cytopathic effect

Objective: To determine whether tears of healthy individuals provide protection against Acanthamoeba-induced cytopathic effect (CPE) in vitro. Methods: Acanthamoebae were added to confluent cultures of corneal epithelium in 24-well plates, and co-cultures were incubated overnight in a serum-free medium containing varying amounts of tears or immunoglobulin A (IgA)-depleted tears. At the end of the incubation period, the cells were stained with Giemsa, and the extent of target cell damage (ie, CPE) was quantified. Results: Acanthamoebae produced extensive CPE. The presence of even a low concentration of tears (10 mu L of undiluted tears per milliliter of media) almost completely inhibited Acanthamoeba-induced CPE. The CPE was inhibited by pretreatment of the parasites with tears. In contrast, the pretreatment of host cells with tears was not protective. This finding suggests that the target of the inhibitory factor is the parasite. IgA-depleted tears also inhibited Acanthamoeba-induced CPE, albeit with a lower potency than total tears. Conclusion: In addition to known IgA-dependent protective factors, human tears contain factors that inhibit Acanthamoeba-induced CPE independently of IgA. Clinical Relevance: Identification and characterization of factors that protect against Acanthamoeba-induced CPE should help in the development of novel, rationally designed strategies to manage and protect against keratitis.