Leukocyte migration across the blood-brain barrier (BBB) is an important step in the progression of brain dysfunction in systemic inflammation. The purpose of this study was to identify the key regulatory molecule(s) at the BBB among the cluster of differentiation (CD) antigens involved in leucocyte migration in lipopolysaccharide (LPS)-induced systemic inflammation based on their absolute protein expressions. Here, we identified the absolute expression levels of 17 CD antigens in isolated brain capillaries (Bcap) of LPS-administered mice. Among them, the expression levels of CD54 and CD106 were dramatically increased in LPS-administered mice compared to the control by 6.21- and 3.67-fold, respectively. In peripheral blood mononuclear cells, the expression levels of CD11a/CD18, the counter-receptor for CD54, were similar to those of CD54 in Bcap of LPS-administered mice. On the other hand, the expression level of CD49d, part of CD29/ CD49d complex, which is the counter-receptor for CD106, was under the limit of quantification. It is thus likely that CD54 at the BBB is predominantly involved in promoting leukocyte migration across the BBB in systemic inflammation. The expression levels of CD9, CD49c and CD97, which are thought to be involved in cell-to-cell interaction, were decreased by 40-60% in Bcap of LPS-administered mice. In contrast, the expression levels of 9 transporters, 2 receptors, and 1 tight junction-related protein in Bcap of LPS-administered mice were essentially unchanged compared to the control. These results suggest that enhancement of leucocyte migration in systemic inflammation involves dynamic changes of CD antigens without alterations of other major functional molecules.
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