Conjunctiva-Associated Lymphoid Tissue – Current Knowledge, Animal Models and Experimental Prospects

Abstract

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.

Development, Alteration and Real Time Dynamics of Conjunctiva-Associated Lymphoid Tissue

“…Recently Liang et al investigated rabbits by means of confocal laser scanning microscopy (CLSM) in order to analyze dynamic processes that occur during inflammation of the ocular surface and its related changes of CALT [37]. As CLSM fails to monitor single cell migration and according velocities inside the tissue in real time, we used intravital two-photon microscopy based on intrinsic tissue autofluorescence with the optional use of fluorescent dyes [3], [12], [27]. This approach enables real time investigation of dynamic immunological processes as demonstrated in lymph nodes and spleen in living animals [38], [39].…”

“…In coherence with well investigated organized lymphoid tissues of the intestine, CALT is thought to represent the immunological interface of the ocular surface with the external environment. It is hypothesized that CALT is in fact responsible for controlled antigen-uptake, -processing and –presentation, followed by initiation of an appropriate immune response and lymphocyte homing [2], [3]. Any reaction to foreign antigen would therefore be based on dynamic processes such as transport of antigen across barriers, cellular migration from, to and within different mucosal compartments and cell-cell interactions.…”

Immunolocalization of Vascular Adhesion Protein-1 in Human Conjunctival Tumors

“…The conjunctiva contains organized lymphoid tissue, which plays a key role in the protection of the ocular surface by initiating and regulating immune responses [1] . ma [9,10] .…”

Ocular Mucosal Immunity

“…The lamina propria contains bone marrow-derived cells that form a mucosal immune system known as conjunctival-associated lymphoid tissue (CALT), a normal, noninflammatory component of the human ocular surface that contributes in the production of immune mediators as well as regulation of the local immune response (Chandler and Gillette, 1983;Kraehenbuhl and Neutra, 1992;Dua et al, 1994;Knop et al, 2008;Knop, 2005a, 2007;Steven and Gebert, 2009). The overlying epithelium is also endowed with intraepithelial lymphocytes (IELs), which balance IEL-mediated production of inflammatory mediators and actively generated immune tolerance.…”