Expression of CZ-1: a CD45RB Epitope on Progenitors of Natural Killer and Other Haematopoietic Cells

CZ-1 is a novel sialic acid-dependent epitope of the murine CD45RB molecule which is expressed on cells that proliferate when cultured in IL-2. Because IL-2 appears to be Important in the differentiation of NK cells, the authors examined the expression of CZ-1 on immature NK-Iineage cells within the bone marrow. All mature NK1.1⁺ cells as well as their NK1. l^? IL-2 responsive precursors were CZ-1⁺. Furthermore, IL-2 unresponsive transplantable NK progenitor cells expressed CZ-1 also. To examine expression of CZ-1 on other immature lymphoid progenitor cells. CZ-1⁺ and CZ-1 marrow cells were tratisplanted Into lightly irradiated scid mice. Transfer of CZ-1⁺ cells resulted iti rapid and sustained generation of thymocytes and splenic B cells, whereas CZ-1^? cells caused delayed repopulation. This suggested that the slowly repoptilating pluripotent stem cells lacked CZ-1. Therefore, expression of CZ-1 on Ly6⁶ Lin^? c-kit⁺ cells, highly enriched for pluripotent stem cells, was examined. This population appeared lo be homogeneously CZ-1^dull. Thus, it appears that expression of CZ-1 is developmentally regulated, with diflerentiation associated with increased expression. Since CZ-1 is expressed on a protein tyrosine phosphatase, it is likely that this molecule regulates differentiation of NK and other lymphoid cells.