PubMedDate not supplied
Using the immunoelectronmicroscopic techniques of Lowicryl embedding and ultracryomicrotomy, the intracellular distribution of HLA class II molecules was investigated on a human B cell line and on human Langerhans cells. These techniques enabled us to localize the HLA class II molecules on fixed specimens in which mobilization or clustering induced by cross linkage with antibodies is ruled out. Compared with Lowicryl embedding, the ultracryomicrotomy clearly showed more labeling. Both in B cells and Langerhans cells, the HLA-DR molecules were predominantly found in intracellular vesicular structures and on the plasma membrane. The HLA-DQ molecules were less abundant than HLA-DR molecules in the B cells and Langerhans cells. In the B cells, HLA-DQ molecules were found on the plasma membrane and in the cytoplasm. In the Langerhans cells, some HLA-DQ molecules were also found in intracellular vesicular structures. These experiments show a different localization of HLA-DR and -DQ antigens both in Langerhans cells and B cells, suggesting a different function for these molecules. The localization of HLA-DR molecules may indicate that these molecules take part in the recycling process of the plasma membrane in B cells and Langerhans cells. The HLA-DQ molecules are not internalized or recycled by the B cells, and a limited internalization of these molecules takes place in Langerhans cells. Finally, no HLA class II or clathrin molecules were found on the Birbeck granules, suggesting that, when no cross-linking with antibodies takes place, Birbeck granules, suggesting that, when no cross-linking with antibodies takes place, Birbeck granules do not play a role in recycling of HLA class II molecules in Langerhans cells.