Higher natural killer cell activity in schizophrenic patients: the impact of serum factors, medication, and smoking.

Schizophrenia has been associated with altered immunity and reduced occurrence of autoimmune diseases and malignancies. A few studies in schizophrenic patients have assessed natural killer cell activity (NKA), but no consistent findings have emerged. However, NKA was assessed using standard procedures and in the absence of autologous serum and the various cytokines that modulate NKA and appear to be abnormal in schizophrenic patients. In the current study, therefore, the number of NK cells and the activity of the individual NK cell were assessed in whole blood shortly after blood withdrawal, in both the presence and the absence of autologous serum. Twenty-nine schizophrenic patients (11 nonmedicated), 8 nonschizophrenic control patients (bipolar and personality disorders), and 31 age-matched healthy controls were studied. Schizophrenic patients showed higher NKA per NK cell than controls and nonschizophrenic patients. This difference remained significant even when the nonmedicated schizophrenics, who showed the highest levels of NKA, were excluded. However, the increase in NKA was more pronounced in the presence of serum and was reduced to an insignificant level when serum was removed from the same samples. In both schizophrenic patients and controls, smokers and women showed lower NKA. Numbers of NK cells did not differ among groups, although medication affected blood concentration of other leukocytes. These findings indicate that the effects of serum factors, psychiatric medication, gender, and smoking should be considered when assessing NKA in schizophrenic patients. The observed higher NKA may help explain the surprising reports of low incidence of lung cancer and other malignancies in schizophrenic patients, despite their higher rate of smoking.