Anatomical, histological and histochemical study of orbital glands of the black winged kite, Elanus caeruleus, and their role in protection of the ocular system

The present study discusses the immune function of the eye glands in a wild bird species. Various methodologies have been utilized in the current study to reveal the anatomical and histochemical qualities of the two glands in the black winged kite. The studied bird possesses small lacrimal gland and large Harderian gland. The lacrimal gland appears as a drop-like shape locates on the ventrolateral surface of the sclera cartilage. While, the Harderian gland is flask shape and lies in the middle of the ventral oblique and pyramidalis muscle. Both eye glands of black winged kite are compound tubuloalveolar type. The alveolar of Harderian gland are lining with simple columnar cells whilst the secretory acini of the lacrimal gland are lining with simple cuboidal epithelium. The histochemical analysis of the two eye glands exhibit that the glands contain neutral and acid mucosubstances. The Immunohistochemical investigation of the two orbital glands showed that the highest concentration population of CD138 positive plasma cells present in Harderian gland especially around the secretory acini and increase in density around the main excretory duct, while, in the lacrimal gland the plasma cells represent the lowest population and found as diffuse singular cells between the secretory acini. This variability of the concentration of plasma cells around the secretory portion of the orbital glands confirms the critical immunity role of the Harderian gland in protecting the ocular surface against any infection, as well as their acidity secretions may significantly inhibit the growth of bacteria and fungi.