Pro-Cognitive Effects of IgM Isotype Anti-NMDAR1 Autoantibodies in Mice

Natural anti-NMDAR1 autoantibodies are present at varying levels in the general human population, but their effects on cognitive function remain unclear. Recent human studies reported significant associations between higher blood levels of natural anti-NMDAR1 autoantibodies and potential neuroprotective outcomes in Alzheimer's disease, traumatic brain injury-associated depression and PTSD symptoms, and schizophrenia. However, whether these natural autoantibodies play a causal role in emotional and cognitive function has not been investigated. Since natural autoantibodies in human blood are predominantly of the IgM isotype, we immunized Aicda mutant mice to produce only IgM isotype anti-NMDAR1 autoantibodies without IgG and IgA isotypes. Mice were tested for sensorimotor gating and conditioned fear and extinction, cross species measures of information processing and emotional memory, respectively. Mice with higher levels of IgM anti-NMDAR1 autoantibodies exhibited significantly increased sensorimotor gating and improved fear extinction recall compared with mice with baseline levels of these autoantibodies. These findings indicate that IgM anti-NMDAR1 autoantibodies are pro-cognitive, unlike previous reports of poor cognition associated with IgG anti-NMDAR1 autoantibodies. Together, these studies suggest that IgM may hold therapeutic potential for a range of neurodegenerative, neurological, and psychiatric disorders.