Conjunctiva-associated lymphoid tissue - current knowledge, animal models and experimental prospects.

The conjunctiva contains organized lymphoid tissue that consists of intraepithelial lymphocytes, subepithelial lymphoid follicles and adjacent lymphatics and blood vessels. This conjunctiva-associated lymphoid tissue (CALT) is assumed to play a key role in the protection of the ocular surface by initiating and regulating immune responses. The article reviews the current knowledge of CALT in humans and compares its structure and functions with mucosa-associated lymphoid tissues at other mucosal sites. An update is given on CALT animal models and on functional studies on the transepithelial transport of microorganisms and antigenic substances by specialized epithelial cells. The use of two-photon microscopy is reviewed regarding its importance to the understanding of dynamic processes going on within CALT.