Morphological and Immunological Characteristics of Conjunctiva-Associated Lymphoid Tissue in Bactrian Camels (Camelus bactrianus)

Abstract

The morphological and immunological characteristics of conjunctiva-associated lymphoid tissue in bactrian camels (Camelus bactrianus) was studied in samples taken from complete conjunctival sacs (n=20) and observed by light microscopy, scanning electron microscopy, transmission electron microscopy, and immunohistochemistry. The CALT in the camel were formed by solitary or aggregate lymphoid follicle, few scattered lymphoid cells, which were mainly distributed in conjunctival fornix. The histological structure of secondary lymphoid follicle was consisted of follicle-associated epithelium (FAE), dome area (DA), follicular area (FA) and parafollicular area (PFA). FAE consisted of flattened associated epithelial cells, microfold cells (M cells) and intraepithelial lymphocytes. The germinal centres of the lymphoid follicles were comprised of lymphoblasts, follicular dendritic cells (FDC), few macrophages and plasma cells. The cytoplasm of these cells contained the usual organelles together with frequent vesicles. Prominent lymph vessels were always presented together with numerous high endothelial venules (HEV). B and T lymphocytes, macrophages were distributed in lymphoid follicle of CALT. The positive FDC were only found in germinal centres. These results suggested that CALT in camel had the cytologic basis of normal mucosa reaction. As an active component of the eye-associated lymphoid tissue in camel, the CALT were inductive sites for the common mucosal immune system, as well as an important components in ocular defense.