C3 and schizophrenia: Research focussing on the association between complement markers and severity of symptoms has reported a positive association between serum levels of C3 and C4 and two items from the Positive and Negative Syndrome scale for Schizophrenia (PANSS) negative symptom scale, referring to active social avoidance and deficient attention, but no associations between complement markers and PANSS positive symptoms (Mayilyan et al., 2008).