BDNF and Cerebral atrophy: When neuroprotective factors, such as nerve growth factor, brain-derived neurotrophic factor (BDNF), neurotrophin 3 (NT-3), and neurotrophin 4/5 (NT-4/5) are deficient in MS patients, the influx of PBMC cells to the CNS can make up for this, slowing the rate of cerebral atrophy.