Emerging evidence for a similar role of glutamate receptors in the nervous and immune systems.

The role of glutamate receptors in synaptic transmission and excitotoxicity in the nervous system is well established. Recent evidence has emerged that glutamatergic mechanisms also exist in a wide variety of non-neuronal cells. In the case of thymocytes and lymphocytes, several types of glutamate receptor are expressed which can induce functional changes. This review focuses on the cellular function of NMDA-activated ionotropic and groups I and III metabotropic glutamate receptors in lymphocytes. Levels of exogenous and endogenous circulatory agonists and antagonists for lymphocyte glutamate receptors, notably homocysteine metabolites, are markedly increased in certain disease states and may be involved in disorders of the immune system. In addition to glutamate and aspartate, these compounds are active at glutamate receptors and increase the excitotoxic effects of glutamate in both neurons and lymphocytes. Increased levels of compounds acting at glutamate receptors may be risk factors for organ damage, for example in both heart and kidney disease. We conclude that glutamate is involved in signaling in immunocompetent cells and that the expression of both ionotropic and metabotropic glutamate receptors may have regulatory functions in immunocompetent cells, as well as in the nervous system. In addition, glutamate may serve as a signaling agent between the immune and nervous systems.