Conjunctiva-associated Lymphoid Tissue (CALT) in Normal and Bordetella avium-infected Turkeys

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Abstract
Conjunctiva-associated lymphoid tissue (CALT) was characterized in normal and Bordetella avium-infected turkey poults during the first 5 weeks of life. At 1, 5, 12, 19, 25, and 33 days post-hatching (DPH), upper and lower eyelids were examined by gross, histologic, and electron microscopic techniques. CALT was confined to the proximal part of the lower eyelid near the conjunctival fornix; it appeared by 5 DPH as individual lymphoid nodules and as dense masses by 19 DPH. In the upper eyelid, CALT was present only as isolated nodules. Histologically. CALT was composed of dense lymphocyte infiltrates within subepithelial connective tissue, intraepithelial lymphocytes, and flattened lymphoid-associated epithelium that lacked goblet cells. Germinal centers were in CALT by 19 DPH. By scanning electron microscopy, epithelial cells over lymphoid areas were flat and had short, irregular microvilli; non-lymphoid areas were covered by cells with tall, regular microvilli. Transmission electron microscopy revealed that with increasing age of birds, the epithelium over conjunctival lymphoid infiltrates became progressively flattened and infiltrated by lymphocytes. Some blood vessels in CALT had high endothelial cells; lymphocytes were in the lumen and between or beneath endothelial cells. In B. avium- infected poults. CALT was increased, developed earlier, and contained more germinal centers than in normal poults. We conclude that CALT of turkeys closely resembles other mucosal lymphoid tissues and may serve as a site for local antigen uptake.