The Distribution of MIC2 Antigen (CD99) Expression on Various Mucosa-Associated Lymphoid Tissue of Human Embryos and Fetuses

Kim, Jung Ran; Lee, Jong Im; Park, Seong Hoe

Abstract

In the present study, we examined to determine the development of various lymphoid tissue including mucosa-associated lymphoid tissue (MALT), thymus, lymph node and liver. In order to investigate the relationship between the morphological events and the expression pattern of MIC2 antigen (CD99) during the development of lymphoid system, we performed the immunohistochemical study using DN16, a monoclonal antibody against MIC2 (CD99), on formalin-fixed and paraffin-embedded lymphoid sections in 68 human embryos and fetuses, between 5 and 39 gestational week (GW). Four neonates, an infant, and 5 adults are also included. CD99 has been expressed along the membrane of hepatocytes and sinusoidal endothelial cells for 10-28 GW, in when the liver the major site of hematopoiesis. In the thymus, CD99 was firstly detected in the presumptive epitheial cells at 10 GW. When the thymus matured and corticomedullary differentiation appeared, CD99 was exclusively expressed in cortical thymocytes. The CD99 expression in epithelial cells of MALT has initiated at 6 GW and 10 GW earlier than that at the onset of MALT development and its expression has been persisted during MALT formation especially 16-25 GW. The finnding that CD99 antigen was expressed in epithelial cells during the development of MALT rnight provide a means to identify a novel epithelial differentiated substance. In addition, endothelial cells that are present in various organs such as liver and small intestine concurrently expressed CD99 antigen and its expression persisted to late fetal period. This point rnight suggest that CD99 antigen regulate the irnigration of lymphocytes from liver, major hematopoietic organ, to thymus or peripheral lyrnphoid organ via the interaction between endothelial cells and lymphocytes.