Aspects of surface membrane differentiation during maturation of human hematopoietic and tumor cells: The 1a system

This chapter focuses on the evidence for the presence of Ia antigens on normal and malignant hematopoietic cells and their role as a surface marker related to differentiation events. It also discusses the occurrence of Ia antigens on certain solid tumors such as malignant melanoma. Ia antigens are selectively distributed as dominant glycoproteins on a limited number of cells. They are restricted both to certain cell lineages and to particular stages of differentiation within the cell series. Yet, at least in the T and B lymphocytes, Ia antigens can be induced with appropriate stimulation and their expression appears to be under flexible control. The period in the differentiation sequence in marrow cells when the Ia antigens are a dominant membrane component is the time when the maximal control of proliferation would be anticipated to occur, suggesting a role for the Ia antigens in this process. This raises the question of interesting parallels between the aspects of the immune response and events in the early stages of hematopoiesis.