Penetration of solutes, viruses, and cells across the blood-brain barrier.

The aspects presented here of how solutes, viruses and cells are able to cross the BBB indicate that there must be an active interaction of endothelium with viruses and immune system cells before they can penetrate the brain and spinal cord. The axoplasmic pathway taken by lectin-solute conjugates is similar but not identical to that followed by viral particles during their retrograde or anterograde transit through the axoplasm. Both the conjugates and virus are transferred to other neurons transsynaptically but the receptor mediated transfer utilized by viruses is far more specific. Cranial nerves are involved in both the entry and egress of antigens into and out of the brain. Antigen, generated within the CNS, may be able to escape from the brain to lymphoid tissue by passing into the fluid around a cranial nerve, thence via the lymph into lymph nodes to initiate an immune response involving the CNS.