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First response: Dendritic cells carry foreign molecules on their surfaces, helping to build an adaptive immune response to infection.
Children with autism have higher levels than controls of dendritic cells, a subset of immune cells, according to a study published 11 October in Brain Behavior and Immunity1.
The study links excess dendritic cells to symptoms of autism and to an enlarged amygdala, a brain region that regulates emotion.
Several studies in the past few years have hinted at a link between autism and a hyperactive immune system. Mothers with high levels of cytokines — molecules that signal to the immune system — or antibodies that attack brain proteins have an increased risk of having a child with autism.
People with autism may express higher levels of certain immune-linked genes. And in a few cases, researchers have seen what look like overactive microglia, the immune cells of the brain, in postmortem brains from individuals with autism.
Dendritic cells are an important link between innate immunity, which responds to all foreign material, and adaptive immunity, which generates a targeted response to certain invaders. Dendritic cells connect the two by presenting foreign molecules to adaptive immune cells, such as T cells.
There are two kinds of dendritic cells: myeloid dendritic cells (mDC), made from progenitors in the bone marrow, and plasmacytoid dendritic cells, which resemble blood cells.
In the new study, researchers looked at the levels of both types of dendritic cells in the blood of 57 children with autism and 29 controls.
On average, children with autism have 25 percent more mDC1 cells — which stimulate T cells — than controls do. They also have 40 percent more rare mDC2 cells , which are believed to fight wound infection.
The researchers found no statistically significant difference between the number of plasmacytoid dendritic cells in children with autism and in controls.
Children in both groups who have more mDC1 cells have larger amygdalae than do those with fewer mDC1 cells, the study found. Elevated levels of myeloid dendritic cells are associated with more pronounced repetitive behaviors (mDC1 cells) and constipation (mDC2 cells).
Even among controls, the children who have the most autism-like behaviors, based on the Vineland Adaptive Behavior scales, are those who also have the highest levels of mDC1, mDC2 and plasmacytoid dendritic cells.
References:
1: Breece E. et al. Brain Behav. Immun. Epub ahead of print (2012) PubMed
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