Lower serum cytokine levels in smokers than nonsmokers with chronic schizophrenia on long-term treatment with antipsychotics

Schizophrenia is associated with various abnormalities in the immune system. Suppression of inflammatory cytokines by cigarette smoke is well-established. The purpose of this study was to determine any differences in cytokine profiles in smokers and nonsmokers with schizophrenia and whether there were any relationships among altered cytokine profiles and psychopathological symptoms. Serum interleukin (IL)-2, IL-6, IL-8, and tumor necrosis factor (TNF)-alpha levels were measured in 96 male inpatients with DSM-IV schizophrenia: 66 smokers and 30 nonsmokers. Symptoms were assessed with the Positive and Negative Syndrome Scale (PANSS). The positive PANSS symptoms were lower in smokers than nonsmokers, while the negative symptoms were lower in those who smoked more cigarettes. Cytokine levels were positively correlated: IL-2 level with IL-6 and IL-6 with both IL-8 and TNF-alpha. Both IL-2 and IL-6, but not IL-8 or TNF-alpha, were significantly lower in smokers than nonsmokers (p < 0.002; p < 0.01). Lower IL-2 levels correlated with fewer negative symptoms and with smoking more cigarettes. The fewer positive symptoms in smokers and fewer negative symptoms in those who smoked more cigarettes may be associated with nicotine-induced suppression of some inflammatory cytokines.