JUL 25, 2008
Toxoplasma gondii, an obligate intracellular protozoan parasite, infects up to 70 percent of the world's population and is a leading cause of infectious posterior uveitis. The invasive form of the protozoa, the tachyzoite, prefers brain and retinal tissue. The tachyzoite may infect the retina by migrating from the brain via the optic nerve, passage of infected monocytes or dendritic cells from the retinal circulation, or direct infection of the retinal vascular endothelium.
The questions of how and why the tachyzoite targets retinal tissue is addressed by this in vitro study, the results of which show that T. gondii tachyzoite are much more efficient at invading human retinal endothelial cells than dermal endothelial cells. To measure invasion efficiency, a type 1 strain of T. gondii that produces a yellow fluorescent protein was used to infect cell cultures of retinal and dermal vascular endothelial cells. When the tachyzoites invaded the endothelial cells, the level of infection was determined by measuring the amount of culture fluorescence.
The high retinal circulation blood flow rate challenges the ability of infectious agents to attach to and invade the retina. However, the results of this study suggest that the specific molecular characteristics of the human retinal vascular endothelium allow the T. gondii tachyzoite to attach to the human retinal endothelial cell, invade the cell membrane and proliferate. The expression of host receptors and the receptor-ligand interactions may underlie the reasons why one cell is preferentially infected over another.
Dr. Wong receives grant support from the National Eye Institute and is employed by Chakshu Research.