Microglia and macrophages in the human pineal gland

BACKGROUND: Over the past two decades, inflammatory responses in the central nervous system (CNS) have been shown to play a role in the etiology of most neurological and psychiatric diseases, as well as in the aging process. Microglia and macrophages are the most important immune cells in the CNS. In contrast to the role of microglia and macrophages in various parts of the CNS, the human pineal gland has not been studied. AIM: To evaluate the morphological characteristics, types and localization of microglial cells in the human pineal gland by immunohistochemistry. MATERIALS AND METHODS: The study was performed using samples of a pineal gland of the human brain obtained in individuals between the ages of 16 and 61 years (n=7). Immunohistochemistry was performed on pineal gland sections using antibodies against Iba1 and TMEM119, selective markers for microgliocytes. Statistical methods were used to evaluate the frequency of immunostained cells. RESULTS: The majority of phagocytic cells identified by immunohistochemistry were found to be microglia and not macrophages. Microglia are represented by both inactive and activated forms. Microglia in the human pineal gland are typically localized in connective tissue trabeculae, both near and far from blood vessels. Microgliocytes are also found in the pineal parenchyma in the hormone-synthesizing cells of the pinealocytes. The number of Iba1 and especially TMEM119 immunoreactive cells decreased significantly with age. CONCLUSION: This study is the first to evaluate microglia and macrophages in the human pineal gland. The prevalence of microglial cells over macrophages was found. The morphological characteristics and localization of the identified microglial cell types suggest their involvement primarily in immune defense and probably also in the regulation of pinealocyte functions. In addition, there are data suggesting the involvement of microglial cells in the development of inflammation in the human pineal gland during aging.