Blood vessels in the brains of more than half of people with autism have an unusually large number of immune cells called T cells, according to a new study conducted by researchers at Beth Israel Deaconess Medical Center in Boston, Massachusetts. The excess of immune cells may damage other cells that form a protective lining for the brain.
This was described as a “chronic inflammatory state” by Matthew Anderson, the study’s lead investigator and chief of neuropathology at Beth Israel Deaconess Medical Center. According to a report this month Spectrum News, Anderson and his team made their finding by chance, during routine microscopic examinations of brain tissue from AutismNet, a repository of brain tissue from people with autism.
During the examination, Anderson said h
e noticed that the samples from autistic people contained numerous round “blebs,” or tiny droplets of debris released from cells. The “blebs” littered the spaces that separate blood vessels from brain tissue.
Following this discovery, Anderson and his team systematically looked for the blebs in samples from 25 people with autism, and 30 non-autistic people, ranged in age from 1 to 68 years old. Eventually, the researchers were able to confirm that the blebs had been released from nearby astrocytes, which are cells that surround blood vessels and form part of the blood-brain barrier. The researchers concluded that the brains of autistic people have much larger areas containing blebs than non-autistic people. The results of the study were published on October 8, in Annals of Neurology.
As noted in Spectrum’s report, cells often release blebs when attacked by immune cells called cytotoxic T cells. About 65% of people with autism have more T cells in the cerebral cortex than those without autism. The study’s findings suggest that the T cells are attacking the astrocytes, though it remains unclear why the T cells accumulate in the autism brain, and why they attack this lining.
For the next phase of their research, Anderson and his colleagues are trying to identify tags on astrocytes that might attract the T cells, and are exploring whether the damage to the barrier occurs in utero.