Ageing and the immune response--a unifying hypothesis?

In this article we review the abnormalities in immune function which have been described in relation to ageing. It is suggested that thymic involution may not be the only underlying cause. Many similar changes can be induced by the endotoxins from the cell walls of Gram-negative bacteria. The colon is a large repository for these organism and bacterial breakdown products are found in portal venous blood. Spillover into the peripheral circulation is prevented by the hepatic Kupffer cells degrading these substances. A waning in Kupffer cell function is well documented in association with ageing and there may be spillover of endotoxins into the peripheral circulation in elderly individuals. It is suggested that such spillover of endotoxins may contribute to some of the immunological changes previously attributed to ageing.