CD68-immunopositive Structures in the Pineal Gland of the Rats Localized Near Blood Vessels

   Introduction. CD68 is a glycoprotein from the family of lysosome-associated membrane proteins. The study of CD68-immunopositive structures in the rat brain’s pineal gland is of particular interest because data on the role of CD68-immunopositive cells and their presence in this neuroendocrine organ, which regulates the body’s circadian rhythm, are contradictory, and the interpretation of their functional role is ambiguous.

   The aim of this study was to identify the most convenient method for immunocytochemical visualization of CD68-immunopositive objects in the rat pineal gland and to determine the localization of the identified structures.

   Materials and Methods. The brain of mature male Wistar rats (n=8) was used for the study. Three primary antibody variants were used: monoclonal antibodies ED1 and KP1 and polyclonal antibodies to CD68.

   Results. The use of monoclonal antibodies KP1 revealed the absence of an immunohistochemical reaction in the rat brain; however, they showed immunoreactivity with the control (human cerebral cortex). Monoclonal antibodies ED1 revealed granules of approximately 0.2 μm in size in the rat pineal gland, forming a dense network in the pineal parenchyma. Granules ranging from 0.3 μm to 2.5 μm in size are located near blood vessels. The granules are primarily located in the central part of the pineal gland; however, their mesh-like distribution limits the ability to characterize the cells themselves. The product of an immunohistochemical reaction using polyclonal antibodies to CD68 is localized discretely throughout the pineal gland as individual granules and their clusters. Granule size ranges from less than 0.2 μm to 4.5 μm, which is comparatively larger than in the case of monoclonal antibodies ED1. The granules are also predominantly located along the vessels.

   Conclusion. Thus, polyclonal antibodies to CD68 are most suitable for detecting macrophages in the rat pineal gland. Clone ED1 yields inconclusive results, and clone KP1 is unsuitable for this purpose. Perivascular localization of cells and granules was detected, indicating that they belong to perivascular macrophages. However, further studies are needed to precisely determine their cellular identity.

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