Olfactory ensheathing cells: unique glial cell types?

Olfactory ensheathing cells (OECs) have recently been shown to have a remarkable ability to repair spinal cord injury. These cells were originally selected for transplant-mediated repair as their inherent behavior in the olfactory system is to support continual regeneration of olfactory receptor neurons throughout life. What is unique about this system is that olfactory receptor neurons, from the PNS are able to extend primary axons from the olfactory mucosa into the central nervous system (CNS) tissue of the olfactory bulb and synapse with second order neurons. This is one of the rare instances of axons crossing from the peripheral neurons system (PNS) into the CNS in the adult animal. In this paper the basic biology of these cells is described, making comparison with another promising candidate for transplant-mediated repair, the Schwann cell. The growth factor requirement for OECs is summarized detailing the influence of these factors on their antigenic and morphological characteristics. Evidence that OECs have distinct glial cell properties is provided with emphasis on their unique ability to interact with astrocytes. A brief background is given of the data obtained using OECs in transplantation studies and the resulting pros and cons discussed with emphasis on limitations of functional recovery.