DALLAS – Imaging mass cytometry is helping researchers to better understand how meningeal inflammation relates to cortical pathology in a subset of multiple sclerosis patients.
This technique for examining multiple proteins within intact tissue and distinguishing cell types based on complex combinations of markers has helped to spot evidence of meningeal inflammation in areas of patient brain samples with cortical gray matter lesions, confirming demyelination and meningeal inflammation observed in experimental allergic encephalomyelitis mouse models.
Imaging mass cytometry “allows us to potentially discriminate microglia from macrophages within brain lesions,” Jennifer Gommerman, PhD, said at a meeting held by the Americas Committee for Treatment and Research in Multiple Sclerosis. “We can look at lymphocytes as well. There’s a lot of potential with this technique, and we’re excited to apply it to the meningeal inflammatory sections of the brain.”
Dr. Gommerman, professor of immunology at the University of Toronto, noted that multiple sclerosis (MS) begins often with a relapsing form of the disease, which tracks with deep white matter lesions that clinicians can image with MRI. “But as the disease progresses, we know that pathology can change, and we can see more pathology in the cortex, including varied bands of demyelination that are adjacent to the meninges,” she said. “This phase of the disease is not effectively treated by therapeutics.”
In this later phase of the disease, she continued, “it’s thought perhaps that the immune system isn’t playing such a big role, but there has been a fair bit of evidence in the literature in recent years that there are in fact immune cells in the brains of people with progressive MS. You can find them in the meninges. They can form clusters of cells within the meninges and they tend to be adjacent to areas of cortical demyelination, suggesting they might be involved in this pathology.”
Dr. Gommerman and her colleagues developed an animal model to evaluate meningeal inflammation in an effort to determine if they can model cortical injury and disease progression. They used an adoptive transfer form of experimental allergic encephalomyelitis in which they prime T cells in SJL mice, remove them, polarize them toward a Th17 phenotype, and transfer them into naive recipients. “When we do this we can see clusters of immune cells forming in the meninges,” Dr. Gommerman said. “They start with T cells but then become overwhelmingly populated by B cells.” Adjacent to these clusters they noted disruption of the glia limitans and demyelination in the cortex. “There’s clearly something going on in the cortex of these animals.”
Mindful that age is one of the most significant predictors of disease progression, the researchers transferred young T cells into mice that were 6-8 months old in addition to animals that were 6-8 weeks old. “Upon sacrifice, the younger mice that got the young T cells had largely resolved their cortical pathology, while the old mice that got the young T cells still showed evidence of demyelination, very angry microglia, and a continual disruption of the glial limitans,” Dr. Gommerman said. “We were able to see axonal stress in comparison to the young mice. We also saw some evidence of synapse loss. It seems that these animals not only have demyelination in the cortex, but there are problems with the axons and the synapses.”
To apply this model in humans, she and her colleagues collaborated with Netherlands Brain Bank in order to obtain brain samples for analysis with imaging mass cytometry, which provides a time-of-flight mass spectrometry readout of the staining pattern of heavy metal ion–tagged antibodies on a single slide-mounted tissue section.
“We really have to be careful which [brain] samples we choose, because not all samples from progressive MS patients have evidence of meningeal inflammation,” she noted. So far, they have observed that meningeal inflammation is associated with gray matter lesions, rather than with normal-appearing gray matter.
“We also need to look at appropriate controls, so our plan is to look at patients who have meningeal inflammation but do not have MS,” she said.
Dr. Gommerman reported having received grants from Novartis, Roche, and Merck, as well as a consulting agreement with Roche.