This article reviews our data on secondary localized corneal amyloidosis after chronic ocular inflammation including trichiasis and keratoconus. Previous findings have suggested that lactoferrin is a precursor protein in secondary corneal amyloidosis. The clinical finding that amyloidosis is frequently observed in female patients also supports a role for lactoferrin as a precursor protein. However, among the whole population with chronic corneal inflammation, the incidence of secondary amyloidosis is low. In this regard, we have identified a genetic polymorphism (Glu561Asp) on the lactoferrin gene in secondary amyloidosis associated with trichiasis. Structural changes may destabilize the local hydrophobic cluster, resulting in exposure of the amyloidogenic region and amyloid fibril formation. On the other hand, this polymorphism was not detected in secondary amyloidosis associated with keratoconus. A different mechanism such as enzymatic digestion might contribute to lactoferrin aggregation. We histochemically analyzed 13 keratoconus specimens obtained at keratoplasty and found lactoferrin protein at corneal epithelial basal cells before amyloid deposition in 3 cases. In some other cases, amyloid was present coincidentally with lactoferrin deposits between basal cells and Bowman membrane. These results suggest that lactoferrin is derived from corneal basal cells. By immunostaining and reverse transcription-polymerase chain reaction, we have shown that human corneal epithelial cells are a putative source of lactoferrin.
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