An immuno-electron-microscopic study of human thymic B cells

Thymic B cells are a constituent of normal human thymic medulla. They are supposed to play a role in T cell maturation. Thymic B cells have been characterized morphologically and immunohistochemically at the light-microscopic level. Their ultrastructural appearance in vivo has not been demonstrated. Six normal infantile thymi were immunolabelled with the pan-B cell marker CD20 using a pre-embedding technique and viewed at the electron-microscopic level. Cells expressing CD20 had long cytoplasmic processes. They were all ”asteroid” in shape and in close contact with thymocytes. Also, their long cytoplasmic processes intermingled with cytoplasmic processes of cells that were presumed to be interdigitating reticulum cells (IDC) based on morphological criteria. Thymic B cells may act in concert with IDC during T cell maturation. Received: 20 October 1995 / Accepted: 10 January 1996