Differential Ia antigen expression by autologous human erythroid and B lymphoblastoid cell lines

Human erythroid precursors express Ia antigens that have serology, function, molecular nature, and genetic regulation that are largely unknown. To approach these issues, Ia+ and Ia- subclones of the HEL human erythroleukemia cell line (HEL-DR+ and HEL-DR-, respectively) and an autologous B lymphoblastoid line (B line) were isolated. These erythroid and lymphoid lines were compared with respect to their binding of monoclonal HLA-D subregion-specific antibodies, the ability to trigger in vitro alloproliferation, expression of class II molecules, and transcription of class II-related genes. Unlike the DP+/DQ+/DR+ B lines, HEL-DR+ differentially expressed DP and DR, but not DQ specificities. Also unlike the autologous B line, HEL-DR+ appeared to be unable to trigger primary or secondary allogeneic T cell proliferation, despite the presence of responder monocytes in these cultures and irrespective of lymphokine addition. HEL-DR+ expression of bona fide class II molecules similar to B line DR heterodimers was verified by two-dimensional gel electrophoresis of material immunoprecipitated from 125I-labeled cells. Northern blot analysis of cytoplasmic RNA from these lines indicated that differential class II gene transcription could readily explain the distinct, lineage-related Ia phenotypes of HEL-DR+ and B line. In addition, the lack of invariant chain and class II transcripts in HEL-DR- implied that expression of these unlinked genes in HEL cells is co-regulated.

Differential Ia antigen expression by autologous human erythroid and B lymphoblastoid cell lines

Human erythroid precursors express Ia antigens that have serology, function, molecular nature, and genetic regulation that are largely unknown. To approach these issues, Ia+ and Ia- subclones of the HEL human erythroleukemia cell line (HEL-DR+ and HEL-DR-, respectively) and an autologous B lymphoblastoid line (B line) were isolated. These erythroid and lymphoid lines were compared with respect to their binding of monoclonal HLA-D subregion-specific antibodies, the ability to trigger in vitro alloproliferation, expression of class II molecules, and transcription of class II-related genes. Unlike the DP+/DQ+/DR+ B lines, HEL-DR+ differentially expressed DP and DR, but not DQ specificities. Also unlike the autologous B line, HEL-DR+ appeared to be unable to trigger primary or secondary allogeneic T cell proliferation, despite the presence of responder monocytes in these cultures and irrespective of lymphokine addition. HEL-DR+ expression of bona fide class II molecules similar to B line DR heterodimers was verified by two-dimensional gel electrophoresis of material immunoprecipitated from 125I-labeled cells. Northern blot analysis of cytoplasmic RNA from these lines indicated that differential class II gene transcription could readily explain the distinct, lineage-related Ia phenotypes of HEL-DR+ and B line. In addition, the lack of invariant chain and class II transcripts in HEL-DR- implied that expression of these unlinked genes in HEL cells is co-regulated.

Subsets of patients with aplastic anemia identified by flow microfluorometry

We used flow microfluorometry to analyze peripheral-blood mononuclear cells from 50 patients with aplastic anemia, to determine whether patients who would recover after immunosuppressive therapy could be distinguished before treatment from those who would not recover. Cells were labeled with murine monoclonal antibodies that are relatively specific for B cells, T cells, T-cell subsets, and monocytes. The data suggested that the number of lymphocytes and the ratios of various subclasses of T cells were not useful in identifying patients who were likely to recover. The complete absence of monocytes was found to identify patients who would not recover, but the presence of monocytes was also sometimes associated with lack of recovery. An unexpected finding was the significant (P less than 0.0001) association between clinical recovery and the presence of a population of small cells (4 to 8 micron) that were phenotypically associated with the erythroid lineage. If this association is confirmed, flow microfluorometry may be useful in selecting the optimal treatment for individual patients with aplastic anemia.

Correlation of two in vitro tests with clinical response to immunosuppressive therapy in 54 patients with severe aplastic anemia

Two in vitro tests were applied to 54 consecutive patients with severe aplastic anemia who were treated in Seattle with antithymocyte globulin. In the first test, peripheral blood mononuclear cells were collected from each patient before antithymocyte globulin therapy and then treated with a panel of monoclonal antibodies and complement. The treated peripheral blood mononuclear cells were assayed for erythroid burst-forming units (BFU-E). This test was designed to determine whether removing various subpopulations of peripheral blood mononuclear cells would increase the number of detectable BFU-E. In the second test, peripheral blood was collected within 48 hr after completion of antithymocyte globulin therapy, and cells were immediately assayed for BFU-E without any further treatment. Data from both tests were analyzed to determine whether the in vitro results correlated with patient response to therapy. Binary logistic regression analyses indicate that a modest correlation (p = 0.04) exists between test 1 in vitro results and patient response to therapy. However, the strength of this association appears to decrease as the interval between diagnosis and treatment increases. In contrast, test 2 had a very significant correlation (p = 0.001) with response to therapy among patients diagnosed more than 1 mo prior to treatment, whereas such an association was not apparent among patients treated within 1 mo of diagnosis.

HLA-DR antigens on lymphoid cells differ from those on myeloid cells

The human HLA-D region-related loci encode antigens which are structurally homologous and functionally analogous to the murine Ia molecules in mice. In addition to a role in immune regulation, it has been shown that the human D region-associated molecules are expressed on immature haematopoietic precursors and may also be involved in the regulation of haematopoiesis. Here we present evidence that distinct 'Ia-like' antigens are found on different haematopoietic cells. Approximately half of the Ia-like molecules expressed by B cells and activated T cells have an 'epitope' which is unique to lymphocytes and is not detectable on the Ia-like molecules of haematopoietic precursors or monocytes. This kind of lineage-restricted variation in Ia expression is a potential basis for selective compartmentalization and regulation of DR-associated function.

Use of an antibody-ricin A-chain conjugate to delete neoplastic B cells from human bone marrow

Affinity-purified rabbit antibody to human lambda and kappa chains (R alpha H lambda kappa) was conjugated to the A-chain of the plant toxin, ricin. The resulting immunotoxin (R alpha H lambda kappa-A) killed cells from the tumor cell line Daudi, which bears surface immunoglobulin, but was nontoxic to the CFU-E, BFU-E, and CFU-GM of human bone marrow. R alpha H lambda kappa-A eliminated 99% of clonogenic Daudi cells that had been mixed with marrow cells in vitro, without demonstrable toxicity to hematopoietic cells. Thus, in vitro treatment of marrow with R alpha H lambda kappa-A may increase the incidence of cure following autologous bone marrow transplantation for the treatment of human B-cell malignancies.

Myeloid-associated differentiation antigens on stem cells and their progeny identified by monoclonal antibodies

Within the hematopoietic system, monoclonal antibodies reactive with antigenic determinants, expressed in a lineage- and stage-restricted fashion, can be used to map myeloid differentiation. We have generated a series of monoclonal antibodies that reacts with myeloid-associated determinants on committed myeloid stem cells and their progeny. Their reactivity with peripheral blood cells was identified by immunofluorescence assays, with bone marrow cells by fluorescence-activated cell sorting, and with committed hematopoietic progenitor cells by both cytotoxic assays and fluorescence-activated cell sorting. Antibody 1G10, which has previously been reported to react with cells of the granulocytic lineage and with a minor subset of mature monocytes, was shown to react with granulocyte-macrophage colony-forming units (CFU-GM). Three antibodies not previously characterized (T5A7, L4F3, L1B2) were shown to react with both granulocytic and monocytic cells and in fluorescence-activated cell sorting studies to detectably stain granulocytic cells at different stages of maturation. These three antibodies also react with CFU-GM, two (L4F3 and L1B2) reacting with all CFU-GM, while T5A7 reacts with only a portion of the day 7 CFU-GM. Antibody L4F3 also reacts with a portion of erythroid burst-forming units (BFU-E). In contrast, the previously reported antibody 5F1, which reacts with monocytic cells, nucleated erythroid cells, and platelets, was shown to react with erythroid colony-forming units (CFU-E). Potential applications of these antibodies to studies of normal and malignant hematopoiesis are discussed.

Modulation of in vitro BFU-E growth by normal Ia-positive T cells is restricted by HLA-DR

The in vitro growth of immature erythroid precursors, assayed as burst forming units (BFU-E), can be enhanced by co-culturing with normal T cells. The growth enhancing effect of normal T cells, however, was shown to be the outcome of at least two functionally distinct subpopulations, one that enhances burst formation and one that limits it. It appears that the T cell population limiting growth enhancement of the erythroid precursors expresses 'Ia-like' antigen (Ia+) because treatment of T cells with anti-Ia antibody and complement significantly increased the ability of the remaining T cells to stimulate antologous BFU-E growth. As BFU-E also seem to express Ia, the inhibiting effect of certain T cells on BFU-E growth may involve the Ia molecule. We show here that the inhibitory effect of Ia+ T cells on BFU-E growth is genetically restricted to cell combinations which are phenotypically identical for at least one HLA-DR (Ia-like) antigen.

Regulation of in vitro erythropoiesis by normal T cells: evidence for two T-cell subsets with opposing function

Cellular interactions responsible for regulating in vitro erythropoiesis were studied using murine monoclonal antibodies recognizing antigens expressed by human mononuclear cells. Cell populations of interest were negatively selected by complement-dependent cytotoxicity and then evaluated for their effect on in vitro growth of erythroid burst-forming units (BFU-E). The data suggest that normal peripheral blood T cells contain at least two functionally distinct subpopulations with opposing regulatory effects: one that enhances burst formation had one that limits burst formation. Whether these effects are mediated by direct interactions of T cells with BFU-E or with auxillary cells remains to be determined.

Erythroid burst forming units (BFUE) grown from canine marrow and peripheral blood

Studies of canine erythropoiesis in vitro have been limited to a relatively mature class of precursor that gives rise to erythroid colonies of 8-64 cells after 2-4 days in culture. In this report we provide data indicating that a second class of erythroid precursor that gives rise to clusters of colonies or bursts can be grown from both dog marrow and peripheral blood. Dog bursts reach maximum size after 7-14 days in culture and have an appearance characteristic of human erythroid bursts. Dog burst forming units, or BFUE, are low density cells (less than or equal to 1.065 g/ml) that can be separated from the majority of colony forming units, or CFUE, by density centrifugation.

Functional subsets of peripheral blood mononuclear cells in transfused dogs separated by size with the fluorescence activated cell sorter

We studied the capability of the fluorescence activated cell sorter (FACS II) to separate, by size, functional subsets of peripheral blood mononuclear cells (PBMC) in normal and transfusion sensitized dogs. PBMC were analyzed for their effect on erythroid colony (EC) growth from marrow of the transfusion donor or unrelated dog. Data indicate that 1) in normal dogs a population of small PBMC which stimulate EC growth could be separated from larger PBMC which had no significant effect on EC, 2) in transfused dogs small PBMC also stimulated EC growth but the large PBMC significantly inhibited EC, and 3) following transfusion-induced sensitization there was an increased number of large PBMC in peripheral blood.

Erythroid colony stimulating and inhibiting cells in peripheral blood of transfused dogs: separation of function by velocity sedimentation

We have previously shown that the addition of normal dog peripheral blood lymphocytes (PBL) to cultures of allogeneic marrow increases the number of marrow-derived erythroid colonies (EC), but that PBL from transfused dogs usually inhibit EC growth from marrow of the transfusion donor. In this study, the cells in normal dog PBL responsible for stimulating EC growth were shown to sediment in a narrow peak at 4.30 mm/hr. A similar population of stimulating cells exists in transfused dogs and can be separated, on the basis of size, from cells that inhibit EC growth. EC-stimulating cells from transfused dog PBL sediment at 3.3--5.0 mm/hr, while cells responsible for inhibition are larger and sediment more rapidly at 5.4--8.1 mm/hr. These data demonstrate that cells capable of stimulating allogeneic EC are present in transfused dogs, but their stimulating ability is masked by the presence of EC-inhibiting cells. Thus, coculture experiments designed to test lymphocyte/marrow cell interactions may miss significant but opposing effects if unfractionated cells are used.