Characterisation of the normal conjunctival leukocyte population

Area of Science:

• Ocular immunology
• Immunohistochemistry
• Mucosal immunology

Background:

• Lymphoid cells are integral to mucosal tissues, forming organized structures like Mucosa-Associated Lymphoid Tissue (MALT).
• Understanding normal conjunctival lymphoid tissue is crucial for studying inflammatory eye conditions.

Purpose of the Study:

• To characterize the leukocyte populations in the normal human tarsal and bulbar conjunctiva.
• To establish a baseline for non-pathological conjunctival immune cells.

Main Methods:

• Immunohistochemistry was employed to analyze conjunctival tissue from healthy individuals.
• Leukocyte subsets, including T cells (CD3+, CD4+, CD8+), B cells, NK cells (CD57+), neutrophils, macrophages, and mast cells, were identified and quantified.

Main Results:

• CD3+ T cells and macrophages were the most abundant leukocytes, present in both epithelium and substantia propria.
• Leukocyte numbers, particularly CD3+ T cells and CD57+ NK cells, were significantly higher in the bulbar conjunctiva compared to the tarsal conjunctiva.
• CD8+ T cells predominated in the epithelium, while CD4+ T cells were more numerous in the substantia propria. CD45Ro+ T cells were prevalent in both compartments.
• Organized conjunctival lymphoid tissue (CALT) was rarely observed, suggesting it may not be universally present in humans.

Conclusions:

• The conjunctiva harbors a distinct leukocyte population with regional variations, potentially reflecting differential antigen exposure.
• The findings provide a foundational understanding of normal conjunctival immunity, essential for diagnosing and managing ocular surface diseases.
• The limited presence of organized CALT challenges the notion of its universal occurrence in humans.