Mucosa-Associated Lymphoid Tissue and Tertiary Lymphoid Structures of the Eye and Ear in Laboratory Animals

Area of Science:

• Immunology
• Ophthalmology
• Otolaryngology

Background:

• Mucosa-associated lymphoid tissue (MALT) in special senses, including the eye and ear, is not well-characterized.
• MALT can be mistaken for non-specific inflammation or tertiary lymphoid structures (TLS).
• Eye-associated lymphoid tissue (EALT) comprises conjunctiva-associated lymphoid tissue (CALT) and lacrimal drainage-associated lymphoid tissue (LDALT), important in humans but less described in animals.

Purpose of the Study:

• To familiarize toxicologic pathologists with MALT in the special senses.
• To provide guidance on differentiating MALT from immune infiltrates or TLS in ocular and auditory tissues.
• To clarify reporting criteria for MALT and TLS in nonclinical studies of the eye and ear.

Main Methods:

• Comparative review of existing literature on MALT and TLS in ocular and auditory systems.
• Analysis of histological features distinguishing MALT from TLS and inflammatory infiltrates.
• Discussion of the development and characteristics of EALT and ear MALT.

Main Results:

• EALT develops postnatally, expands with antigen exposure, and forms lymphoid follicles.
• Distinguishing between MALT and TLS is crucial, especially in the context of inflammation (e.g., otitis media).
• Lymphoid aggregates in healthy ocular tissues require further etiological investigation.

Conclusions:

• Accurate identification and reporting of MALT and TLS in the special senses are essential for toxicologic pathology.
• Understanding MALT development and its distinction from TLS aids in interpreting nonclinical study findings.
• This review provides a framework for consistent reporting of immune-related findings in the eye and ear.