Maintenance of granulocyte-monocyte progenitor cells in liquid cultures of human foetal liver

Defective erythropoiesis in primary myelofibrosis associated with a chromosome 11 abnormality

A case of primary myelofibrosis was identified with a previously unreported complex karyotype with two abnormal clones in addition to a proportion of normal cells: 46,XY,-2,-11, + der(2)t(2;11) (q24/31;q13), + mar and 45,XY,-2,-11, + der(2)t(2;11)(q24/31;q13), + mar, -17, del(7q). Study of circulating committed progenitors from this patient consistently showed (1) an absence of erythroid progenitors which is uncommon and (2) greatly increased granulocyte-monocyte progenitors (CFU-GM) which is generally observed in myelofibrosis. Further study showed that peripheral blood mononuclear cells co-cultured with irradiated normal bone marrow stroma generated increased numbers of CFU-GM compared with controls but failed to generate erythroid progenitors, providing evidence for an intrinsic defect in erythropoiesis. Only once previously has the absence of erythroid progenitors in primary myelofibrosis been studied in relation to cytogenetic abnormalities. This case also revealed a complex karyotype which, however, shared with our case a defect on chromosome 11. The identification of two cases of primary myelofibrosis which lack committed erythroid progenitor cells and which show in common a chromosomal defect on chromosome 11 point to the existence of genes on this chromosome which play a key role during erythropoiesis.

Allorecognition of HLA-DR and -DQ transfectants by human CD45RA and CD45R0 CD4 T cells: repertoire analysis and activation requirements

We have investigated the requirements for allogeneic stimulation of human CD4 T cells using HLA class II products expressed on various cellular backgrounds. Human (class II-negative RJ2.2.5 mutant) B cell lines transfected with HLA-DR or -DQ cDNA clones were efficient stimulators for highly purified CD4 T cells. HLA-DR-transfected mouse L cells or IFN-gamma-induced human fibroblasts, although able to function as accessory cells for T cell responses to the mitogen PHA, failed to stimulate strong T cell alloresponses. On the basis of these observations, we have employed class II transfectants to address the following questions: (a) do CD45RA and CD45R0 subpopulations differ in their allogeneic activation requirements, (b) are these subpopulations skewed in their recognition of HLA-DQ vs. HLA-DR in a manner which might support the concept that CD45RA T cells are involved in HLA-DQ-restricted suppressor inducer functions and (c) by using transfectants expressing individual HLA-DR or -DQ heterodimers in combination with limiting dilution analysis, can one for the first time obtain estimates of precursor frequencies for allogeneic cells recognizing each of these class II isotypes? Our results show that CD45RA and CD45R0 T cells respond comparably to optimal numbers of stimulator cells. However, when CD45RA and CD45R0 T cell populations depleted of endogenous accessory cells were cultured with limiting numbers of stimulator cells, CD45R0 cells generally responded more strongly, consistent with the elevated levels of various adhesion molecules known to be expressed by this population. Further, we found a similar representation of responses to HLA-DR and -DQ antigens among populations expressing CD45RA and CD45R0 isoforms. Finally, the precursor frequencies of allogeneic CD4 T cells responding to particular HLA-DR alleles were higher than to -DQ, but only by a factor of about 1.6, indicating that HLA-DQ recognition may occur more frequently than implied from previous antibody blocking studies.

Phorbol myristate acetate treatment of normal human myeloid blast cells promotes monopoiesis and inhibits granulopoiesis

Fractionation of mononuclear cells from human fetal liver provides a cell population at early stages of myeloid differentiation which, when cultured, generates neutrophils and macrophages for up to a month. These studies describe the further purification of an undifferentiated myeloid blast cell population by rosette sedimentation of unwanted cells, after coating these cells with monoclonal antibodies which identify macrophages and erythroblasts. In culture, the purified blast cells generated only neutrophils and macrophages. When treated with 10 nM PMA, 62% of the purified cells were induced to differentiate towards macrophages within 48 h. PMA-induced cells acquired morphological features of macrophages and synthesized alpha-naphthyl acetate esterase. The differentiation of the remaining blast cells towards neutrophils, seen in untreated cultures, was completely inhibited by PMA, as revealed by the absence of increases in the numbers of cells expressing lactoferrin and an antigen which appears at the promyelocyte stage of differentiation. Thus, PMA effects intracellular changes which both promote monopoiesis and inhibit granulopoiesis, suggesting a reciprocal interaction between intracellular processes which regulate the capacity for the two pathways of maturation. The purified blast cell population provides a good model system for studies of molecular events which regulate the expression of macrophage characteristics.

Liver-associated macrophage precursor cells proliferate under impairment of regular hemopoiesis

We reported previously that immature macrophage precursor cells can be isolated from spleen and liver of cyclophosphamide or pyran copolymer-pretreated mice. We now extended our investigations to livers of normal, untreated specific pathogen-free mice. Using the response to the macrophage growth factor colony-stimulating factor-1 (CSF-1) and the presence of the mouse macrophage-specific F4/80 antigen as criteria of definition, in the liver of normal mice we could demonstrate macrophage precursor (M phi P) cells by means of proliferation assays and flow cytometric analysis. The amount of M phi P present in the normal liver was significantly increased after administration of pyran copolymer. Also an enhanced proliferative response to CSF-1 as well as augmented natural killer activity and cytostasis of Candida albicans was noted in liver nonparenychymal cells (LNPC) after treatment of bone marrow (BM)-irradiated, splenectomized mice with pyran copolymer. Since the irradiated BM was actually proven to be silent by assessment of BM number and proliferative capacity and by scoring white blood cells, our findings suggest a response of endogenous liver M phi P under the applied conditions. Further evidence for the presence of endogenous liver hemopoietic cells was obtained from transplantation experiments in which LNPC brought about the survival of lethally irradiated mice. The data point towards a significance of the liver in disposing hemopoietic cells to the organism under impairment of regular hemopoiesis.