A Monoclonal Brain-Reactive Antibody Leads to ASD-like Phenotype in Male Mice

Background:  Maternal brain-reactive antibodies have been associated with increased risk for Autism Spectrum Disorders (ASD) in the offspring. These antibodies can affect the fetal brain before it develops a competent blood brain barrier that prevents exposure to antibody. Approximately 10% of women with a child with ASD have brain-reactive antibodies, while these antibodies are present in 2% only of unselected women of child bearing age.

Objectives:  We generated brain-reactive monoclonal antibodies (Mabs) from mothers of a child with ASD who harbored a positive serology in order to study their antigenic specificities and to determine which antibodies contribute to ASD pathogenesis

Methods: Memory (CD27+) B cells from the blood of women of a child with ASD previously shown to have brain-reactive antibodies were incubated with fetal human brain homogenate that had been labeled with biotin.  B cells bound to fetal human brain antigens were isolated using EasySep Biotin selection kit (StemCells technologies). Single CD27+ B cells are then sorted into PCR plates and immunoglobulin heavy and light chain variable region genes were amplified by PCR and expressed in HEK 293 cells. Antigenic specificity of brain-reactive Mabs was studied using a human protein array and a cell based assay.  The C6 Mab was injected into pregnant mice at E13.5. Effects of in-utero exposure on brain and behavior were analyzed during embryonic stage and in adulthood.

Results: One brain-reactive Mab, C6, targets two proteins in the potassium channel complex, a subunit of potassium channel (KCNAB2) and Caspr2; both have been previously linked to ASD. When C6 was administrated to pregnant mice on day E13.5 male but not female fetal brain showed  thinning of the cortical plate and fewer mitotic cells (PH3 staining) at E15.5 compared to control embryos  of mice injected with a non-brain reactive Mab. When pregnancies were allowed to reach full term, male but not female mice exposed in-utero to C6 displayed increased stereotypic behavior in the marble burying test, spent less time near a fellow mouse in the social preference test and showed impaired spatial flexibility memory in the clock maze test. Consistent with the latter observation, we found decreased dendrites and spines in the hippocampus of these mice.   

Conclusions: We show in a mouse model that in-utero exposure to a monoclonal anti-brain reactive antibody isolated from a mother of an ASD child induces neurodevelopmental deffects in the offspring that can be observed already during the embryonic stage. This work demonstrates that maternal anti-brain antibodies lead to in-vivo brain and behavior alterations. Identifying more pathogenic brain-reactive Mabs can yield additional disease mechanism.