Multiple lines of evidence demonstrate that the immune system, in particular, lymphoid cells, play an important role in drug addiction. Destruction of the immune system with irradiation or immunosuppressive drugs has been shown to significantly alleviate the opiate-withdrawal syndrome (39,40). In contrast, transfer of lymphoid cells to irradiated rats before morphine administration restores drug-withdrawal signs (41). These findings suggest a mechanism for neuro-immunological interactions, where factors derived from the immune system may regulate functions of the central nervous system, influencing addictive behaviors. This mechanism is supported by the discovery of functional synapses between neurons and lymphocytes (42). Given that IL15 is an important immunoregulatory cytokine influencing activation and proliferation of T lymphocytes and natural killer cells, it appears reasonable to speculate that IL15 influences smoking addiction through its immunoregulatory effects.
