Nerve growth factor and inflammation: a complex bidirectional interaction

The nervous and immune systems share common functions: both are involved in adapting the body to the environment and in maintaining homeostasis. Because they are the two major adaptive systems of the body it is not surprising that they have developed common strategies: both are able to sense external and internal variations, which are signalled to specialised cells causing the activation of specific and rapid responses. Through these well orchestrated responses the two systems not only restore homeostasis but retain the memory of the "danger" so that faster and more specific reactions will be triggered after subsequent similar challenges to homeostasis. To be able to orchestrate a strictly integrated response, the two systems should act simultaneously, communicate with each other and work together to eliminate danger and restore homeostasis [1]. Thus, for a more efficient control of the internal environment, cross-talk between the nervous and immune systems, based on close anatomical connections [2,3] common chemical signals and specific receptors [4-6], is needed to sense challenge to the host, monitor immune activity and activate neuronal pathways and regulatory loops [7,8]. Among the growing number of molecules known to be involved in both neuronal and immune modulation, Nerve Growth Factor (NGF) seems to have a role in this complex network of bi-directional signals between the nervous and immune systems.