Increased activation product of complement 4 protein in plasma of individuals with schizophrenia

Agnieszka Kalinowski, Joanna Liliental, Lauren A. Anker, Omer Linkovski, Collin Culbertson, Jacob N. Hall, Reenal Pattni, Chiara Sabatti, Douglas Noordsy, Joachim F. Hallmayer, Elizabeth D. Mellins, Jacob S. Ballon, Ruth O’Hara, Douglas F. Levinson, Alexander E. Urban

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


Structural variation in the complement 4 gene (C4) confers genetic risk for schizophrenia. The variation includes numbers of the increased C4A copy number, which predicts increased C4A mRNA expression. C4-anaphylatoxin (C4-ana) is a C4 protein fragment released upon C4 protein activation that has the potential to change the blood–brain barrier (BBB). We hypothesized that elevated plasma levels of C4-ana occur in individuals with schizophrenia (iSCZ). Blood was collected from 15 iSCZ with illness duration < 5 years and from 14 healthy controls (HC). Plasma C4-ana was measured by radioimmunoassay. Other complement activation products C3-ana, C5-ana, and terminal complement complex (TCC) were also measured. Digital-droplet PCR was used to determine C4 gene structural variation state. Recombinant C4-ana was added to primary brain endothelial cells (BEC) and permeability was measured in vitro. C4-ana concentration was elevated in plasma from iSCZ compared to HC (mean = 654 ± 16 ng/mL, 557 ± 94 respectively, p = 0.01). The patients also carried more copies of the C4AL gene and demonstrated a positive correlation between plasma C4-ana concentrations and C4A gene copy number. Furthermore, C4-ana increased the permeability of a monolayer of BEC in vitro. Our findings are consistent with a specific role for C4A protein in schizophrenia and raise the possibility that its activation product, C4-ana, increases BBB permeability. Exploratory analyses suggest the novel hypothesis that the relationship between C4-ana levels and C4A gene copy number could also be altered in iSCZ, suggesting an interaction with unknown genetic and/or environmental risk factors.

Original languageEnglish
Article number486
JournalTranslational Psychiatry
Issue number1
StatePublished - 22 Sep 2021

Bibliographical note

Publisher Copyright:
© 2021, This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply.


Dive into the research topics of 'Increased activation product of complement 4 protein in plasma of individuals with schizophrenia'. Together they form a unique fingerprint.

Cite this