Do circulating OKT6-reactive cells belong to Langerhans cell lineage?

A few studies have been made in characterizing the phenotype, ontogeny, ultrastructure, and cytochemistry of circulating cord blood cells. Such studies have been hampered by the difficulty in obtaining pure populations of these cells. We therefore sought to obtain T6-positive cell-enriched populations from human cord blood using panning method. In cord blood, dendritic OKT6-labeled cells were classified in two types: some were similar to lymphocyte-like cells and some were consistent with monocyte-like cells. Both types lacked intracytoplasmic Birbeck granules. Homogeneous labeling of HLA-DR antigens were observed in both types. Heterogeneous labeling of T6 antigen was observed in both types. The monocyte-like cells have developed Birbek granule-like structures after exposure to OKT6 and immuno-adherence. The results suggest several different putative lineages of these OKT6-reactive cells: early precursors of dendritic cells, immature neonatal lymphoid subsets, and immature macrophagic leukocytes.