Immunohistochemical localization of vitronectin, its receptor and beta-3 integrin in Alzheimer brain tissue

The vitronectin receptor (VNR) is an integrin which consists of an alpha-subunit which can associate with multiple beta-subunits. A polyclonal antibody to this integrin weakly stained resting microglia in white matter of control brain and strongly stained reactive microglia in both gray and white matter of Alzheimer brain. This antibody, as well as a monoclonal antibody to beta 3, stained some platelets in capillaries of both control and Alzheimer tissue. When the antiserum was immunoabsorbed with a preparation enriched in the alpha-chain of the vitronectin receptor, it failed to stain microglial cells, but continued to stain platelets. When it was immunoabsorbed with a peripheral blood platelet preparation, all immunostaining was abolished. These results indicate that the vitronectin receptor of microglia is associated with a beta-chain different from beta 3, but that beta 3 is expressed by some platelets in brain capillaries. An antibody to vitronectin itself stained senile plaques and neurofibrillary tangles in Alzheimer entorhinal cortex, but only residual plasma in control tissue. Senile plaques positive for vitronectin had microglial cores strongly positive for the vitronectin receptor. The high levels of vitronectin receptor on reactive microglia in areas containing extracellular vitronectin suggest the possibility that vitronectin is serving an opsonizing function for microglial phagocytosis.