While inflammation in the brain is a component of schizophrenia and bipolar disorder’s neuropathology, researchers have found differences in immune cell activity and highlighted potential for new treatments.

Neuroscience Research Australia (NeuRA) PhD candidate Gerardo Mendez-Victoriano led the research, which explored immunomarkers in the brain to understand the changes in schizophrenia and bipolar disorder, with the report published in Brain, Behaviour and Immunity as ​“Midbrain microglial and macrophage mRNAs distinguish neuroinflammatory schizophrenia from bipolar disorder”.

Mr Gerardo Mendez-Victoriano, said the research looked at the diagnostic changes in the brain’s immune cells – microglia and macrophages – in the ventral midbrain to see how similar or distinct these were in schizophrenia compared to bipolar disorder.

“Neuroinflammation is a component of what we find in the brains of people who have had schizophrenia or bipolar disorder,” he said.

“From what we already knew about inflammation-related markers we expected to see a different direction or magnitude of change in brain immune cells between schizophrenia and bipolar.

“We studied the brain’s immune cells and found that while microglia and macrophages are activated in both diseases, the activation is different. In schizophrenia we see increased motility, in bipolar disorder there was a distinct, possibly suppressed, inflammatory state in the mid-brain.

“This helps explain why anti-inflammatory treatments don’t work the same everyone and means future treatments may need to be tailored differently for each condition.”

The study used transcriptomics and functional immunomarkers to test for diagnostic changes in specific transcripts commonly used to differentiate microglia and macrophages and examined ventral midbrain of 61 healthy controls, 63 cases of schizophrenia and 33 cases of bipolar disorder. Researchers evaluated the mRNA levels of the microglial/​macrophage markers grouped according to the associated functions of their encoding proteins, immune complex antigen binging-triggered activation, inflammatory activation and enzymatic activity in the midbrains of people with schizophrenia or bipolar disorder compared to controls overall and when stratified by low and high-inflammation subgroups.

Around 50% of schizophrenia and 30% of bipolar patients have a high-inflammation profile. These inflamed cases show the most functional/​cognitive and neuroanatomical/​structural MRI changes, including reduced memory, attentional and verbal impairment, and a reduction in brain volume/​cortical thickness.

“The inflammation-triggering event could be from external or internal sources, but further research is needed to identify triggers for brain immune cell changes,” Mr Mendez-Victoriano said.

“We need to continue exploring why the immune cells behave differently, test treatments that target the specific immune pattern in each disorder and develop ways to detect these inflammatory differences in living patients.”

You can read the full paper here.