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Impression Cytology of the Lid Wiper Area
Published on: August 9, 2016
Morphological evidence of M cells in healthy canine conjunctiva-associated lymphoid tissue
Elizabeth A Giuliano1, Cecil P Moore, Thomas E Phillips
1Department of Veterinary Medicine and Surgery, University of Missouri, Columbia, MO 65211-7400, USA.
Insights
Canine conjunctiva-associated lymphoid tissue (CALT) contains M cells in the follicle-associated epithelium (FAE) that are analogous to those in other mucosa-associated lymphoid tissue (MALT). These CALT M cells can bind and transport bacteria, suggesting potential for ocular disease research and delivery systems.
Area of Science:
- Immunology
- Veterinary Ophthalmology
- Cell Biology
Background:
- The eye's immune system relies on specialized tissues like conjunctiva-associated lymphoid tissue (CALT).
- Mucosa-associated lymphoid tissue (MALT) in other areas contains M cells crucial for immune surveillance.
- The presence and function of M cells in canine CALT have not been fully characterized.
Purpose of the Study:
- To investigate the follicle-associated epithelium (FAE) and lymphoid nodules of dog nictitating membranes.
- To determine if canine conjunctiva-associated lymphoid tissue (CALT) possesses M cells similar to those found in other MALT regions.
Main Methods:
- Harvesting and examining nictitating membrane lymphoid follicles from healthy dogs via light, transmission electron, and scanning electron microscopy.
- Treating some dogs with a topical bacterial suspension before euthanasia to assess M cell function.
- Performing immunohistochemistry to analyze lymphocyte populations within the CALT.
Main Results:
- The FAE overlying CALT exhibited M cell morphology, including an attenuated apical surface and basolateral pockets containing lymphocytes.
- CALT M cells were observed to bind and internalize heat-killed bacteria.
- Immunohistochemistry revealed B-cell germinal centers and T-cell caps in the lymphoid tissue beneath the FAE.
Conclusions:
- Canine CALT shares morphological and functional similarities with MALT in other mucosal sites, particularly regarding M cells.
- The identification of canine conjunctival M cells is significant for understanding ocular diseases.
- These findings suggest potential applications for CALT M cells in ocular vaccination and drug delivery strategies.
Purpose:
To characterize the follicle-associated epithelium (FAE) and organized lymphoid nodules from dog nictitating membranes to determine if canine conjunctiva-associated lymphoid tissue (CALT) contains M cells analogous to those described in other regions of mucosa-associated lymphoid tissue (MALT).
Methods:
Nictitan lymphoid follicles from 15 healthy dogs (30 eyes) were harvested immediately post-mortem. Twelve follicles from each nictitating membrane were isolated. Four follicles from each eye of 10 dogs were examined by light microscopy, transmission electron microscopy and scanning electron microscopy. Five of the 10 dogs were treated with a heat-killed staphylococcal topical suspension immediately prior to euthanasia. Nictitan follicles from five other dogs were processed for immunohistochemistry to characterize follicle lymphocyte populations.
Results:
The FAE overlying CALT demonstrated morphology characteristic of M cells, including attenuated apical cell surface with blunted microvilli and microfolds, invaginated basolateral membrane forming a cytoplasmic pocket containing lymphocytes and macrophages, and diminished distance between the apical and pocket membrane. Heat-killed bacteria were bound to the surface and transcytosed to the cytoplasmic pocket of CALT M cells. Immunohistochemistry of organized lymphoid tissue subtending the FAE demonstrated B-cell germinal centers with T-cell predominant apical caps.
Conclusions:
In canine CALT, the FAE overlying lymphoid follicles, as well as the distribution of T and B lymphocytes subtending this region, contain morphologic and functional features analogous to MALT described in other regions. Documentation of canine conjunctival M cells is of clinical relevance in the study of primary ocular diseases, as well as a potential means of vaccination or drug delivery.
