increased natural killer cells activity in schizophrenic patients

background: schizophrenia has been associated with altered immunity. different studies regarding natural killer cell activity (nka) in schizophrenic patients have shown inconsistent results. objectives: to evaluate nk cell activity in schizophrenic patients in comparison with healthy control individuals.   methods: 30 medication-free schizophrenic patients and 41 healthy sex, age and smoking status matched individuals were included in this study. nk cell activity of case and control subjects was measured by methyl-thiazol-tetrazolium (mtt) test. statistical analysis of the data was done using spss 11.5 software.   results: nk activity of patients and normal subjects had a mean of 36.94 ± 26.15 (mean ± sd) and 22.31 ± 17.92, respectively. a significant increase in nk activity in schizophrenic patients compared to controls (p = 0.011). among patients, nk activity of smokers was significantly lower than that of non-smokers (p = 0.02). other demographic factors didn't show any influence on nk activity.   conclusion: the higher activity of nk cells in the schizophrenic patients as compared with the control population could explain the low incidence of cancer in these patients. decreasing the effect of smoking on nk activity in the patients could be one of the responsible factors for the inconsistency in the results of different studies.