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Erich Knop, Nadja Knop; Lacrimal Drainage–Associated Lymphoid Tissue (LDALT): A Part of the Human Mucosal Immune System. Invest. Ophthalmol. Vis. Sci. 2001;42(3):566-574. doi: https://doi.org/.
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purpose. Mucosa-associated lymphoid tissue (MALT) specifically protects mucosal
surfaces. In a previous study of the human conjunctiva, evidence was
also found for the presence of MALT in the lacrimal sac. The
present study, therefore, aims to investigate its morphology and
topographical distribution in the human lacrimal drainage system.
methods. Lacrimal drainage systems (n = 51) obtained from
human cadavers were investigated by clearing flat wholemounts
or by serial sections of tissue embedded in paraffin, OCT compound, or
epoxy resin. These were further analyzed by histology,
immunohistochemistry, and electron microscopy.
results. All specimens showed the presence of lymphocytes and plasma cells as a
diffuse lymphoid tissue in the lamina propria, together with
intraepithelial lymphocytes and occasional high endothelial venules
(HEV). It formed a narrow layer along the canaliculi that became
thicker in the cavernous parts. The majority of lymphocytes were T
cells, whereas B cells were interspersed individually or formed
follicular centers. T cells were positive for CD8 and the human mucosa
lymphocyte antigen (HML-1). Most plasma cells were positive for IgA and
the overlying epithelium expressed its transporter molecule secretory
component (SC). Basal mucous glands were present in the lacrimal
canaliculi and in the other parts accompanied by alveolar and acinar
glands, all producing IgA-rich secretions. Primary and secondary
lymphoid follicles possessing HEV were present in about half of the
conclusions. The term lacrimal drainage–associated lymphoid tissue (LDALT) is
proposed here to describe the lymphoid tissue that is regularly present
and belongs to the common mucosal immune system and to the secretory
immune system. It is suggested that it may form a functional unit
together with the lacrimal gland and conjunctiva, connected by tear
flow, lymphocyte recirculation, and probably the neural reflex arc, and
play a major role in preserving ocular surface integrity.
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