Increased S100B+ NK cell counts in acutely ill schizophrenia patients are correlated with the free cortisol index, but not with S100B serum levels

Several studies have provided evidence for increased S100B serum concentrations in schizophrenia. The pathophysiological significance of this finding is still uncertain because S100B is involved in many cellular mechanisms and is not astrocyte-specific as was previously assumed. S100B is also expressed by subsets of CD3+ CD8+ T cells and natural killer (NK) cells and may therefore be linked to the immune hypothesis of schizophrenia. We have quantified S100B+ CD3+ CD8+ T cells and NK cells by flow cytometry in the peripheral blood of 26 acutely ill schizophrenia cases and 32 matched controls. In parallel, S100B concentrations and the free cortisol index (FCI), a surrogate marker for stress axis activity, were determined in serum samples from the same blood draw. Psychopathology was monitored using the Positive and Negative Syndrome Scale (PANSS). The patient group had increased S100B+ NK cell counts (P=0.045), which correlated with the FCI (r=0.299, P=0.026) but not with the PANSS or the elevated (P=0.021) S100B serum concentrations. S100B+ CD3+ CD8+ T cell counts were not significantly changed in the patient group and did neither correlate with the FCI and PANSS, nor with S100B serum concentrations. In conclusion, despite the observation of an increase in S100B+ NK cells in schizophrenia patients, the lack of a correlation with serum S100B concentrations suggests that these cells are probably not a major source of S100B in the blood of schizophrenia patients. Notably, elevated S100B+ NK cell counts may be linked with stress axis activation.