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Characterization of membranous (M) cells in normal feline conjunctiva-associated lymphoid tissue (CALT)
Elizabeth A Giuliano1, Kevin Finn
1Department of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia, MO 65211, USA. giulianoe@missouri.edu
Insights
Researchers identified membranous (M)-cells in feline conjunctiva-associated lymphoid tissue (CALT), similar to those in other mucosal tissues. This finding is significant for understanding feline eye diseases and potential therapeutic applications.
Area of Science:
- Veterinary Ophthalmology
- Immunology
- Cell Biology
Background:
- Conjunctiva-associated lymphoid tissue (CALT) plays a role in ocular immune responses.
- Mucosa-associated lymphoid tissue (MALT) in other species contains specialized M-cells within the follicle-associated epithelium (FAE).
- The presence and function of M-cells in feline CALT remain largely uncharacterized.
Purpose of the Study:
- To investigate the presence of M-cells in the FAE of feline CALT.
- To characterize the morphology of lymphoid nodules in the nictitans of healthy cats.
- To determine if feline CALT contains M-cells analogous to those in other MALT regions.
Main Methods:
- Examination of lymphoid follicles from the nictitans of 10 healthy cats using light, transmission electron, and scanning electron microscopy.
- Isolation of lymphoid nodules from the third eyelid using a surgical microscope.
- Immunohistochemistry to identify T- and B-lymphocyte distribution beneath the FAE.
Main Results:
- The FAE overlying feline CALT exhibited M-cell morphology, including attenuated apical surfaces and basolateral cytoplasmic pockets.
- Electron microscopy confirmed characteristic M-cell features.
- Immunohistochemistry revealed B-cell rich germinal centers and T-cell rich interfollicular zones.
Conclusions:
- Healthy feline CALT possesses morphologic features consistent with M-cells found in other MALT.
- The identification of feline conjunctival M-cells is clinically relevant for studying ocular diseases.
- Feline conjunctival M-cells may offer potential for targeted vaccination or drug delivery strategies.
Objective:
To characterize conjunctival lymphoid nodules obtained from the nictitans of healthy cats to determine if the follicle-associated epithelium (FAE) of conjunctiva-associated lymphoid tissue (CALT) in this species contains membranous (M)-cells analogous to those described in other regions of mucosa-associated lymphoid tissue (MALT).
Methods:
Lymphoid follicles from nictitan bulbar surfaces of 10 healthy cats (20 eyes total) were examined. Nictitans from five cats were harvested immediately post-mortem and a minimum of 12 lymphoid nodules from each third eyelid were isolated using a Zeiss operating microscope. At least three lymphoid follicles from each eye were examined using light microscopy (LM), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) using standard fixation and embedding protocols. Nictitan-lymphoid follicles from another five healthy cats were processed for immunohistochemistry to characterize the distribution of T- and B-lymphocytes present beneath the FAE.
Results:
The FAE overlying CALT from 10 healthy cats demonstrated morphology characteristic of M-cells including attenuated apical cell surface with blunted microvilli and microfolds, invaginated basolateral membrane forming a cytoplasmic pocket, and diminished distance between the apical and pocket membrane. Immunohistochemistry of lymphoid tissue subtending the FAE demonstrated B-cell dependent regions in the germinal centers surrounded by T-cell dependent interfollicular zones.
Conclusions:
Healthy feline CALT contains morphologic features analogous to those described in other regions of MALT. Documentation of feline conjunctival M-cells is of clinical relevance in the study of primary infectious, allergic, and autoimmune ocular diseases, as well as a potential means of vaccination or drug delivery.
