Low-affinity NGF-receptor and E-N-CAM expression define two types of olfactory nerve ensheathing cells that share a common lineage.

Previously, we have shown that the O4 antibody can be used to define and purify olfactory nerve ensheathing cells (ONECs) from the rat olfactory bulb by fluorescence-activated cell sorting. In this study, using a larger panel of neural markers, we demonstrate that this apparently homogeneous population of ONECs possess a heterogeneous antigenic profile both in vivo and in vitro. The antigenic profile of the sorted cells initially correlated with their antigenic profile in vivo, although expression of some of the markers was either lost or gained during time in culture. These changes were influenced by the culture conditions, with a greater loss of "typical" ONEC markers in serum-containing medium. In serum-free medium, which maintains the cells in a phenotype that closely resembles their in vivo counterparts, we were able to reclassify the ONECs into two cell types based on morphology and antigenic phenotype by using antibodies to polysialic acid (correlating with the embryonic form of N-CAM expression) and the low-affinity nerve growth factor receptor. A detailed immunocytochemical study of the developing olfactory system showed that these two cell types could also be detected along the entire length of the olfactory nerve and the outer layer of the olfactory bulb from Embryonic Day 14 to adulthood, suggesting they were not an in vitro artefact. To address the relationship between the two cell types we constructed a clonal ONEC cell line by retroviral infection with the temperature-sensitive mutant gene of the large T antigen. This clonal cell line contained cells that expressed antigenic phenotypes of both classes of ONECs, suggesting that both cell types are related and share a common lineage.