Comparative Anatomy and Immunohistochemical Study of Eyelids in Two Different Avian Species: Expression of CD20+, CD138+ and CD1a+ Cells in the Mucosa of the Eyelid

ABSTRACT The objective of this study was to discuss the influence of the environment on the macro–microstructure features of the eyelids of two birds: hooded crow, Corvus cornix , and Muscovy duck, Cairina moschata , which also show lymphoid follicles, lymphocytes and some immune cells in the eyelid mucosa and their effect on healthy eyes. In both birds, numerous lymphocytes were distributed within connective tissue in the tarsal and orbital regions of the lower eyelid, and lymphoid follicles were located mostly beneath the conjunctival tissue near the tarsal plate to form a part of diffuse conjunctiva‐associated lymphoid tissue. There were no lymphoid follicles in the upper eyelid or nictitating membrane of the crow. However, they appeared in the nictitating membrane of the duck. In the crow, CD1a‐positive cells were marked in the skin and CD20‐positive population was detectable as a small patch in the intrafollicular, while in the duck, few CD1a‐positive cells were scattered in the stroma and there was a weak reaction around the feather follicle, while a densely positive CD20 was found in the paracortex and medullary regions of the follicle and in the stroma beneath the skin, also around blood vessels and HEV in both birds. CD138+ cells are scattered in the stroma and their population increases around blood vessels and HEV. In the third eyelids, CD20+, CD138+ and CD1a+ show an increase in concentration around blood vessels, with plasma cells having the highest density, while the lowest population of CD20+ is dispersed as singular cells between the two membrane surfaces. Thereby, these changes in the morphology of the upper, lower and third eyelids were strongly related to the lifestyle of the birds.