Our findings confirm the presence of an inflammatory syndrome in patients with first-episode of psychosis, in the absence of Th1/Th2 ratio changes.

Interestingly, the finding of elevated levels of IL-1α, IL-6 and TNF-α, both in serum and leukocytes gene expression analyses, provides direct evidence that the immune cells are affected in psychosis, and suggests that the peripheral blood immune cells are the main source of these cytokines’ elevated levels in the serum. In contrast, IL-1β and IL-8 were elevated in the serum but not in leukocyte gene expression analyses. This is in agreement with other studies finding discrepancies between serum cytokine levels and cytokine mRNA levels in peripheral blood mononuclear cells (PBMCs) in other populations (O’Rourke et al., 2006). This difference may be the result of abnormalities in post-transcriptional regulation of cytokine expression, leading to a lack of correlation between transcript levels and protein levels. Moreover, gene expression may be more easily and rapidly affected than systemic cytokine levels (Futh et al., 2004), and therefore some differences between gene expression and serum levels might be related to the effects of more recent and acute vs chronic activation of the immune system. Alternatively, peripheral blood immune cells are not the primary source of IL-1β and IL-8 elevated serum levels in these patients. Indeed, elevated cytokines may derive from cytokine-producing cells other than peripheral immune cells, such as intra-hepatic or adipose tissue-associated cells (O’Rourke et al., 2006). In our study, we matched our patients and controls for body mass index, in order to minimize the effect on a potential excess of abdominal adipose tissue on inflammatory markers in patients. However, individuals with identical BMI may have different body compositions with regard to fat and muscle, so we cannot exclude a role of the adipose tissue or of other lymphoid or non-lymphoid cells in contributing to the elevated levels of IL-1β and IL-8 found in our patients. Indeed, increased intra-abdominal fat deposition has been previously reported in depressed patients who did not differ for BMI from the comparison healthy control group (Thakore et al., 1997).

Interestingly, the fact that cytokine expression differs between the serum and gene expression analyses is also reflected in the pattern of associations between serum or leukocytes mRNA cytokines levels and psychosocial and clinical factors. For example, both serum and gene expression levels of TNF-α are elevated in patients, but only serum levels correlate with a history of childhood trauma. This could be again explained by the effects of a long-lasting chronic activation of the immune system, affecting serum levels. This notion is consistent with our previous studies finding an association between a history of childhood trauma and peripheral inflammation in adults (Danese et al., 2007, 2008) as well as children (Danese et al., 2010). In contrast, only leukocytes mRNA levels correlate with a higher number of recent life events, suggesting that more recent stressors are needed to activate immune cells.

The presence of a pro-inflammatory state at the onset of psychosis supports the role of increased inflammation in the development of psychosis. Indeed, previous studies have shown that cytokines can affect the synthesis, release and reuptake of neurotransmitters as well as influence neurogenesis (Miller et al., 2009; Raison and Miller, 2011; Zunszain et al., 2012a,b). In particular, it has been recently shown that IL-1β exerts a negative effect on human hippocampal neurogenesis, by activating the kynurenine pathway and subsequently affecting the availability of tryptophan and the production of enzymes conducive to neurotoxic metabolites (Zunszain et al., 2012a). Moreover, preclinical studies have suggested that pro-inflammatory cytokines could directly reduce gene transcription of brain-derived neurotrophic factor (BDNF), further supporting a role of inflammation in influencing neuroplasticity (Murphy et al., 2000). Interestingly we have recently shown that stressful events can influence BDNF expression at the onset of psychosis, and that this association is possibly mediated by an inflammatory pathway (Mondelli et al., 2011).

Our preliminary findings support the hypothesis that childhood trauma and recent stressors contribute to the pro-inflammatory state shown in patients with psychosis. In particular, we found that childhood trauma and recent stressors increase levels of pro-inflammatory cytokines (TNF-α, IL-1β, INF-γ, IL-6) and chemokines (MCP-1) in either patients or controls, and decrease levels of the growth factor VEGF in the patients’ group. It is unclear why psychological stress would affect specific cytokines without apparently affecting others, or why stress would affect different cytokines in patients and in healthy controls. Indeed, the association between childhood trauma and increased levels of TNF-α has been already recently reported in patients with schizophrenia (Dennison et al., 2012), while this is the first time that childhood trauma has been found to be associated with increased levels of MCP-1 and decreased levels of VEGF in patients with psychosis. MCP-1 is a pro-inflammatory chemokine known to play a major role in the development of cardiovascular disease by promoting the recruitment of leuokocytes to sites of inflammation in the vessel wall (Hansson and Hermansson, 2011). On the other hand, VEGF is known to have neurotrophic and neuroprotective actions; low serum VEGF levels have been associated with Alzheimer’s disease, suggesting their role in a possible neurodegenerative process (Mateo et al., 2007). Indeed, further studies would need to confirm these preliminary results and further investigate whether, and why, psychological stress affects only specific cytokines.

Our exploratory analyses also showed an association between current nicotine use and higher IL-6 serum levels but not IL-6 mRNA levels, suggesting that the increased IL-6 production by the PBMCs cannot be explained by current nicotine use. Cigarette smoking has been recently shown to have selective effects on serum components of patients with schizophrenia that lead to altered immune function different from healthy controls (Herberth et al., 2010). This might partly explain the specific effect of nicotine use on IL-6, and the lack of its effect on cytokine levels in our group of healthy controls. Our findings of lower IL-1α and IL-2 levels associated with current cannabis use are not surprising, and are consistent with previous pre-clinical and clinical studies showing an anti-inflammatory effect of cannabinoids (Klein and Cabral, 2006). Interestingly, we also found that cannabis use was associated with higher levels of MCP-1 in our patients. One previous study has demonstrated that a cannabinoid agonist induces a modulation of specific chemokines, such as IL-8 and MCP-1, but not of other chemokines (GRO-α and MIP-1α), indicating a possible specific molecular targeting of cannabinoid agonists (Jbilo et al., 1999).

Some limitations of the study need to be acknowledged. First, for the second aim of the study we conducted multiple correlation analyses in a relatively small sample of subjects. However, these should be considered explorative analyses, reporting preliminary findings which will need to be validated by future studies. Secondly, our subjects were non-fasting at time of blood sampling and the time of blood sampling was random during the day. However, patients and controls did not appear to differ significantly for time of blood sampling, and the blood sample for serum and mRNA levels was taken at the same time point for each subject. Moreover, our group of patients was heterogeneous for diagnosis, since it included both patients with schizophrenia-like and affective psychosis. However, a diagnostic heterogeneity is typical in first-episode psychosis, since patients are at the beginning of their illness, and it represents better what we would expect in a clinical setting. Last, most patients were taking antipsychotic treatment, although for a short period of time, and this could have confounded some of our findings. However, we did not find a correlation between duration of antipsychotic and cytokine levels in our patients.

In conclusion, first-episode psychosis patients are characterised by a pro-inflammatory state that appears mainly mediated by activation of the PBMCs; however, other peripheral tissues (such as hepatic or adipose tissue) also seem to contribute to this inflammatory syndrome. Stressful events, both in childhood and closer to psychosis onset, appear to contribute to the increased cytokine production in first-episode psychosis.