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Impressum
Concept of an Eye-Associated Lymphoid Tissue (EALT) composed of the Conjunctiva, Lacrimal Gland und Lacrimal Drainage System
Knop E., Knop N.
Abt. für Zellbiologie in der Anatomie, Medizinische Hochschule Hannover, D- 30625 Hannover
Objective: Our previous findings show that the normal human conjunctiva
as well as the lacrimal drainage system have a mucosa-associated lymphoid
tissue which is referred to as CALT and LDALT, respectively. Therefore
in the present study we addressed the question how these organs fit in
the known immune protection provided by the lacrimal gland.
Methods: 53 conjunctival sacs, 51 lacrimal drainage systems and
24 lacrimal glands from human body donors were investigated by a combined
analysis of translucent conjunctival wholemounts together with section
morphology, immunohistology and electron microscopy.
Results: All conjunctival sacs and lacrimal drainage systems had
a diffuse lymphoid tissue composed of lamina propria lymphocytes (LPL),
intraepithelial lymphocytes (IEL), mostly IgA-positive plasma cells and
occasional interspersed high endothelial venules (HEV). The overlying
epithelium was strongly positive for the immunoglobulin transporter SC.
In addition there was follicular organized lymphoid tissue in 60% of the
complete conjunctival sacs and in about half of the lacrimal drainage
systems. This consisted of accumulations of B cells and peripheral T-cell
zones with HEV. The overlying follicle-associated epithelium (FAE) consisted
of flat cells with similarity to antigen transporting M-cells. In the
lacrimal gland our techniques could confirm the presence of fewer lymphocytes
and numerous mostly IgA-producing plasma cells around the IgA- and SC-positive
epithelium of the acini. This tissue was found to be continuous from the
lacrimal gland through its excretory ducts into the conjunctiva and from
there via the lacrimal canaliculi into the lacrimal drainage system.
Conclusion: Our results show that a mucosa-associated lymphoid
tissue occurs continuously at the normal ocular surface and in the associated
mucosal tissues and glands. Therefore we propose the concept of an Eye-
Associated Lymphoid Tissue (EALT). These organs presumably have a differential
function because the lacrimal gland has the largest capacity to produce
immunoglobulins whereas the conjunctiva and lacrimal drainage system can
additionally detect antigen and prime respective plasma cells.