Immunobiology of acanthamoeba keratitis

Acanthamoeba keratitis (AK) is remarkably rare, even though the causative agent can be isolated from virtually any environmental niche and the leading risk factor for corneal infection - contact lens wear - is practiced by over 30 million individuals in the United States. This might lead one to suspect that immunity is effective and commonplace. However, with the exception of immunoglobulin A antibodies in the tears, the adaptive immune system is incapable of preventing or eliminating corneal Acanthamoeba infections. Interestingly, primitive elements of the innate apparatus - namely macrophages and neutrophils - are first responders that effectively prevent and resolve corneal Acanthamoeba infections in experimental animals, and possibly in humans as well.