Can an afferent arm to the immune response originate within the brain?
How safe viral vector gene transfer into the brain is, depends on whether viral vector injection leads to a systemic immune response. Dendritic cells, the central cells in stimulating the afferent arm of the immune response, are localized within the skin, heart, or lung, but not the naïve brain.12 Under immune-stimulatory and inflammatory conditions, they take up antigen and transport it to secondary lymphoid organs where they prime naïve T cells. Whether this process of antigen transport to lymph nodes can occur in the brain is one of the central unresolved issues remained to be answered definitely, in order to understand completely the physiology of the brain’s immune system.13 However, brain perivascular macrophages and microglial cells originate from the bone marrow and are slowly turned over by circulating precursors originating in the bone marrow. It has been postulated that these cells could carry particulate antigens to the draining lymph nodes. However, even though some report
