Cyclosporin A as an Alternative Neuroimmune Strategy to Control Neurites and Recover Neuronal Tissues in Leprosy.

Leprosy, also known as Hansen's disease, continues to have a substantial impact on infectious diseases throughout the world. Leprosy is a chronic granulomatous infection caused by Mycobacterium leprae and shows a wide clinical and immunopathological spectrum related to the immune response of the host. This disease affects the skin and other internal organs with a predilection to infect Schwann cells, which play an active role during axonal degeneration, affecting peripheral nerves and promoting neurological damage. This chronic inflammation influences immune function, leading to neuroimmune disorders. Leprosy is also associated with neuroimmune reactions, including type 1 (reverse) and type 2 (erythema nodosum leprosum) reactions, which are immune-mediated inflammatory complications that can occur during the disease and appear to worsen dramatically; these complications are the main concerns of patients. The reactions may induce neuritis and neuropathic pain that progressively worsen with irreversible deformity and disabilities responsible for the immunopathological damage and glial/neuronal death. However, the neuronal damage is not always associated with the reactional episode. Also, the efficacy in the treatment of reactions remains low because of the nonexistence of a specific treatment and missing informations about the immunopathogenesis of the reactional episode. There is increasing evidence that peripheral neuron dysfunction strongly depends on the activity of neurotrophins. The most important neurotrophin in leprosy is nerve growth factor (NGF), which is decreased in the course of leprosy, as well as the presence of autoantibodies against NGF in all clinical forms of leprosy and neuroimmune reactions. The levels of autoantibodies against NGF are decreased by the immunomodulatory activity of cyclosporin A, which mainly controls pain and improves motor function and sensitivity. Therefore, the suppression of anti-NGF and the regulation of NGF levels can be attractive targets for immunomodulatory treatment and for controlling the neuroimmune reactions of leprosy, although further studies are needed to clarify this point.