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Reactive changes of interstitial glia and pinealocytes in the rat pineal gland challenged with cell wall components from gram‐positive and ‐negative bacteria

Abstract:  Lipopolysaccharide (LPS), the major proinflammatory component of gram‐negative bacteria, is well known to induce sepsis and microglial activation in the CNS. On the contrary, the effect of products from gram‐positive bacteria especially in areas devoid of blood–brain barrier remains to be explored. In the present study, a panel of antibodies, namely, OX‐6, OX‐42 and ED‐1 was used to study the response of microglia/macrophages in the pineal gland of rats given an intravenous LPS or lipoteichoic acid (LTA). These antibodies recognize MHC class II antigens, complement type 3 receptors and unknown lysosomal proteins in macrophages, respectively. In rats given LPS (50 μg/kg) injection and killed 48 h later, the cell density and immunoexpression of OX‐6, OX‐42 and ED‐1 in pineal microglia/macrophages were markedly increased. In rats receiving a high dose (20 mg/kg) of LTA, OX‐42 and OX‐6, immunoreactivities in pineal microglia/macrophages were also enhanced, but that of ED‐1 was not. In addition, both bacterial toxins induced an increase in astrocytic profiles labelled by glial fibrillary acid protein. An interesting feature following LPS or LTA treatment was the lowering effect on serum melatonin, enhanced serotonin immunolabelling and cellular vacuolation as studied by electron microscopy in pinealocytes. The LPS‐ or LTA‐induced vacuoles appeared to originate from the granular endoplasmic reticulum as well as the Golgi saccules. The present results suggest that LPS and LTA could induce immune responses of microglia/macrophages and astroglial activation in the pineal gland. Furthermore, the metabolic and secretory activity of pinealocytes was modified by products from both gram‐positive and ‐negative bacteria.