Journal of anatomy
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The effects of bacterial lipopolysaccharide (LPS) on the expression of surface antigens including major histocompatibility complex (MHC) and complement type 3 (CR3) receptors on microglial cells in the corpus callosum in postnatal rat brain were investigated. When LPS was injected intravenously (i.v.) in 1-d-old rats, the immunostaining of callosal amoeboid microglial cells with OX-18 directed against MHC class I antigen was enhanced 24 h after the injection in comparison with the controls. The expression of MHC class II (Ia) antigen on the same cell type as shown by its immunoreactivity with OX-6 was also elicited especially after 2 intraperitoneal (i.p.) injections of LPS. ⋯ The effect of LPS on the expression of CR3 on amoeboid microglial cells was not obvious after a single injection, but the immunoreactivity with OX-42 was also augmented in rats given 2 i.p. administration of LPS into rats at 1 an 4 d of age. It is concluded from this study that the expression of MHC class I and class II antigens on amoeboid microglial cells in corpus callosum was upregulated and induced respectively after i.v. or i.p. injection of LPS into early postnatal rats. Although relatively fewer in number when compared with OX-18 and OX-42 positive cells, it is suggested that the OX-6 positive cells would have the potentiality to function in antigen presentation in the postnatal rat brain when challenged by the endotoxin.