Acanthamoeba spp. secrete a mannose-induced protein that correlates with ability to cause acanthamoeba keratitis

by Hurt, Michael Allen.

Abstract (Summary)
Acanthamoeba spp. are ubiquitously distributed in the environment. The trophozoite form can infect the cornea and cause sight-threatening corneal inflammation known as Acanthamoeba keratitis. The pathogenic cascade of Acanthamoeba keratitis begins when Acanthamoebae bind to mannose expressed on traumatized corneas. Published reports indicate that mannose is upregulated on the corneal surface during wound healing. Experiments in laboratory animals have shown that corneal abrasion prior to infection is essential for generating Acanthamoeba keratitis. Furthermore, supernatants from Acanthamoeba vi trophozoites grown in medium supplemented with mannose were found to be more toxic to corneal cells than from those without mannose. After binding to mannose ligands, the amoebae desquamate the corneal epithelial cells, perforate the Bowman’s membrane, and invade the corneal stroma. Once inside the stroma, the amoebae secrete collagenolytic factors that dissolve the stromal matrix. Collectively, these data suggest that binding to mannose induces Acanthamoeba trophozoites to secrete cytotoxic factors necessary for causing keratitis. The data showed that mannose induced A. castellanii to secrete a novel 133 kDa protein that is cytolytic to corneal epithelial cells. Cytolytic activity of the mannose-induced protein (MIP-133) was abrogated with the addition of serine protease inhibitors, indicating that MIP-133 is a serine protease. Examination of the cytolytic mechanism revealed that cell death was due to the activation of the caspases-3 and -10-dependent apoptotic cascade. Incubations of MIP-133 with artificial Bowman’s membrane and stromal matrix demonstrated that MIP-133 degraded the collagen comprising the bulk of these layers. Analysis of Acanthamoeba spp. revealed that production of MIP-133 correlated with ability to cause keratitis. Soil isolates neither made MIP-133 nor produced significant keratitis. All clinical isolates examined produced MIP-133 and keratitis in laboratory animals. Anti-MIP-133 antibodies neutralized the cytolytic and collagenolytic activity of MIP- 133 in vitro. Additionally, incubations of anti-MIP-133 with whole trophozoites inhibited their migration through an extracellular matrix. vii Oral immunization with MIP-133 resulted in reduced severity and duration of Acanthamoeba keratitis. Mucosal antibodies isolated from orally immunized animals inhibited cytolytic activity in vitro. Furthermore, oral immunization in animals with existing chronic Acanthamoeba keratitis (mimicking human disease) displayed immediate reduction in disease severity and mitigation of corneal disease. viii
Bibliographical Information:


School:The University of Texas Southwestern Medical Center at Dallas

School Location:USA - Texas

Source Type:Master's Thesis

Keywords:dissertations academic acanthamoeba keratitis corneal diseases mannose immunization texas


Date of Publication:01/01/2003

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