Development of Human Lymphohematopoiesis Defined by CD34 and CD81 Expression

Abstract

Human blood cells, except for erythrocytes and platelets, express CD81, a member of the transmembrane 4 superfamily (TM4SF). CD81 is also expressed on most of human immature hematopoietic cells, CD34 + cells, which are divided into three populations according to the expression of CD34 and CD81; CD34 + CD81 +, CD34 + CD81 High and CD34 Low CD81 +. Myeloid and lymphoid progenitors exist in the CD34 + CD81 + population, and megakaryocytic progenitors are only in CD34 Low CD81 + population. Erythroid and multipotential progenitors are shared by CD34 + CD81 + and CD34 Low CD81 + populations, but multipotential progenitors in the CD34 + CD81 + population have already lost most of their myeloid potential. NK cells and mast cells can be generated from all three populations. Long-term repopulating (LTR) lymphohematopoietic stem cells are present in the CD34 + CD81 + population. Based on these findings, we propose a model for the development of CD34 + CD81 + lymphohematopoietic stem cells. Along the differentiation cascade from CD34 + CD81 + lymphohematopoietic stem cells, there appear to be pathways to CD34 Low CD81 + or CD34 + CD81 High cells, even if they are indirect. CD34 Low CD81 + pathways define the loss of LTR ability, and lymphoid and myeloid potentials, whereas CD34 + CD81 High pathways represent the exclusive commitment to NK cells and mast cells.