The structure and function of conjunctiva-associated lymphoid tissue in chickens and turkeys

Fix, Andrew
Journal Title
Journal ISSN
Volume Title
Research Projects
Organizational Units
Veterinary Pathology
Organizational Unit
Journal Issue

The morphology of conjunctiva-associated lymphoid tissue (CALT) was studied in chickens and turkeys by gross, light microscopic, and electron microscopic techniques. Additional studies, using carbon, iron oxide, and latex beads, characterized particle uptake by CALT and statistically evaluated computerized image analysis findings;Although not present at hatching, CALT developed in the lower eyelid of turkeys and chickens in association with longitudinal conjunctival folds and fissures. During the first week, CALT appeared as lymphoid nodules that expanded conjunctival folds. A statistically significant increase in CALT was demonstrated during the post-hatching period. Fewer isolated nodules were evident in the upper eyelid conjunctiva. Lymphoid nodules were composed of lymphocytes, lymphoblasts, macrophages, and germinal centers. The epithelium was flattened, contained intraepithelial lymphocytes, lacked goblet cells, and formed a lymphoepithelium with a discontinuous basement membrane. Vessels evident at the base of lymphoid nodules had high endothelial cells and adherent intraluminal lymphocytes. In addition, chronic antigenic stimulation induced by bacterial conjunctivitis in turkeys produced hyperplasia in CALT;The capacity for transepithelial particle uptake was verified by light microscopy using carbon, iron oxide, and latex beads. Clustering within subepithelial macrophages was characteristic after uptake. Uptake increased with tracer contact time and was more extensive in older birds. The site of tracer uptake varied with particle size, occurring superficially along lymphoepithelial folds for smaller particles but deeper within fissures for larger particles. Using computerized image analysis, a statistically significant increase in uptake was demonstrated between 5 and 15 minutes of tracer contact time and between 3 and 5 weeks of age;These studies document the similarity in structure and function between CALT and other mucosal lymphoid tissues. Therefore, CALT likely has a role in paraocular and upper respiratory immunity in turkeys and chickens.

Veterinary pathology