Suppression of B lymphocyte genesis in the bone marrow by systemic graft-versus-host reactions

The effects of systemic graft-versus-host (GVH) reactions on B lymphocyte production in the bone marrow of mice were examined by quantitating populations of pre-B cells and B lymphocytes. Acute and chronic GVH reactions were induced by injecting A strain lymphoid cells into either (C57BL/6 X A) F1 or (CBA X A) F1 mice, respectively. Control groups of F1 hybrid mice were given syngeneic lymphoid cells. By double immunofluorescence labeling for cytoplasmic mu heavy chains of IgM (c mu) and for surface mu (s mu) the absolute numbers of pre-B cells (c mu + s mu-) and B lymphocytes (s mu +) in the bone marrow and spleen were determined. During acute GVH reactions, the pre-B cells and B lymphocytes in the bone marrow fell rapidly in numbers and were almost absent from 16 days until the end of the 30-day experimental period. In the spleen, the number of B lymphocytes remained normal for 8 days, then fell to less than 2% of control values from 16 days onward. A similar initial decline in pre-B cells and B lymphocytes occurred during chronic GVH reactions. In long-term survivors of GVH reactions, pre-B cells and B lymphocytes began to reappear after 40 days and maintained normal numbers from 100 to 150 days. The antibody response of spleen cells to sheep red blood cells was lost during GVH reactions. However, this occurred even before B lymphocytes were eliminated and the response remained subnormal after B lymphocyte numbers had recovered. The results demonstrate that systemic GVH reactions markedly depress the normally active genesis of primary B lymphocytes in the bone marrow of the host, accounting in part for the associated state of humoral immunodeficiency.

Phenotype and proliferation of early B lymphocyte precursor cells in mouse bone marrow

Bone marrow cells were examined by double immunofluorescent labeling techniques to detect determinants for the B lineage monoclonal antibody, 14.8, the nuclear enzyme, terminal deoxynucleotidyl transferase (TdT), cytoplasmic mu chains (c mu), and surface mu (s mu). In 8-9-wk-old C3H/HeJ mice, 14.8+ cells totalled 22.2% of all marrow cells (35 X 10(5) cells/femur). While many 14.8+ cells were c mu+ s mu- pre-B cells and s mu+ B lymphocytes (17.0%), the remainder (5.2%) were large cells lacking mu chains. After injecting vincristine sulfate, these 14.8+ mu- cells accumulated in mitosis at a rate of 13.5%/h (turnover time, 7.4 h). Their calculated total production rate (41 X 10(6) cells/whole marrow/d) exceeded that previously determined for large pre-B cells, suggesting some cell loss from the B lineage. TdT+ cells made up 1.8% of marrow cells and were mainly medium-sized cells. They all lacked mu chains, but half (0.9%) bound 14.8 antibody at low to medium intensity. Three discrete cell populations were thus defined, differing in mean cell diameter TdT+ 14.8- mu-, 9.5 micron; TdT+ 14.8+ mu-, 10 microns; and TdT- 14.8+ mu-, 11.5 micron, presumptively representing a sequence of cell stages preceding the expression of mu chains in large pre-B cells (TdT- 14.8+ c mu+ s mu-, 11.5 microns). This work provides a tentative model of early progenitor cells and their proliferation in normal marrow as a basis for studies of perturbations and the control of B lymphocytopoiesis.

Population dynamics of bone marrow B lymphocytes

The dynamic concepts of lymphocyte populations which heralded the era of modern cellular immunobiology have been generally substantiated by recent studies and are still being correlated with functional properties. B lineage cells in the bone marrow are dynamically heterogeneous: A large majority are newly-formed, rapidly renewed cells, continuously produced from precursor cells within the bone marrow and disseminated during a terminal maturation phase via the blood stream. These cells develop low densities of sIgM in the extravascular bone marrow parenchyma and may undergo some further maturation within bone marrow sinusoids. The rate of production of bone marrow B cells appears to depend partly on the total load of exogenous agents to which the individual is exposed. Bone marrow lymphocyte production maintains a population of rapidly renewed virgin B cells in the peripheral lymphoid tissues. A small proportion of these cells apparently may be selected to enter a long-lived pool of B cells if suitably activated. By continuously creating novel clonotypes this process potentially can anticipate new antigen challenges and allow the immune system to build up a repertoire of antigen specificities most appropriate to the individual's changing environment throughout life. A minority of B lymphocytes in the bone marrow comprises slowly renewed, long-lived cells which enter and leave the bone marrow parenchyma as a selective part of the recirculating lymphocyte pool in the blood stream. Their role in the bone marrow is unknown. They include antigen-specific B memory cells, yet these are not activated within the bone marrow itself. No regulatory role has yet been directly demonstrated. Recently activated B cells enter from the spleen after secondary antigenic stimulation to develop into antibody-producing cells within the bone marrow. In assessing the significance of any phenotypically or functionally distinct B cell subset in the bone marrow, a basic consideration is to assign the subset to one of the foregoing dynamic categories. Within a given category cells may represent one stage in a time sequence of development. The bone marrow also produces lymphocytes of as yet uncertain lineage and contains selected subsets of T cells. The roles of these cells in cytotoxic, regulatory, or other events remain to be elucidated.

Regulation of bone marrow lymphocyte production: IV. Altered kinetic steady state of lymphocyte production after chronic changes in exogenous stimuli

A transient increase in B lymphocyte production in mouse bone marrow has previously been shown to follow a single administration of various exogenous agents. The effect of sustained changes in exogenous stimuli on the level of bone marrow B lymphocyte production has now been studied. In mice given multiple injections of sheep red blood cells (SRBC) for four weeks the production of bone marrow lymphocytes was augmented, as indicated by increased numbers of cytoplasmic mu-chain-bearing pre-B cells and of surface mu-chain-bearing B lymphocytes, as well as increased rates of pre-B cell proliferation and small lymphocyte turnover. In an attempt to reduce potential external stimuli, mice were raised on an elemental diet. When compared to conventionally reared mice, however, they showed little difference in bone marrow small lymphocyte production and an identical pre-B cell proliferation rate. In addition, the small lymphocyte production rate in the thymus was not consistently altered either in SRBC-treated mice or elemental diet-fed mice, whereas small lymphocyte renewal in the spleen showed changes reflecting those in the bone marrow. The results demonstrate that a chronic increase in exposure to extrinsic agents can produce a long-term elevation of the population size and production rate of bone marrow B lineage cells. This suggests that the level of the kinetic steady state of primary B lymphocyte production normally observed in the bone marrow may reflect the level of exposure to potential stimulants in the external environment.

Mechanism of altered B-cell response induced by changes in dietary protein type in mice

The effect of 20 g/100 g dietary lactalbumin (L) or casein (C) diets or a nonpurified (NP) diet on the immune responsiveness of C57Bl/6J, C3H/HeJ and BALB/cJ mice has been investigated by measuring the response to the T cell-independent antigen, TNP-Ficoll. To investigate the possible influence of dietary protein type on the supply of B lymphocytes, bone marrow lymphocyte production has been examined by a radioautographic assay of small lymphocyte renewal and an immunofluorescent stathmokinetic assay of pre-B cells and their proliferation. The humoral response of all mice fed the L diet was found to be higher than that of mice fed the C diet or nonpurified diet. A similar pattern of dietary protein effect in (CBA/N X DBA/2J) F1 mice carrying the xid defect was observed following challenge with sheep red blood cells (SRBC). An even greater enhancing effect of dietary L was noted in normal (DBA/2J X CBA/N) F1 mice after immunization with SRBC, but in contrast, the normal large-scale production of B lymphocytes in mouse bone marrow was independent of the type of dietary protein. Dietary protein type did not affect blood level of minerals and trace metals. The free plasma amino acid profile essentially conformed to the amino acid composition of the ingested protein, suggesting that the changes in plasma amino acid profile might be a crucial factor in diet-dependent enhancement or depression of the B-cell response.(ABSTRACT TRUNCATED AT 250 WORDS)

B lymphocyte production in the bone marrow of mice with X-linked immunodeficiency (xid)

CBA/N mice carry an X-linked recessive immunodeficiency (xid) gene manifested by the absence of a B lymphocyte subpopulation, but the manner in which the xid gene exerts its effect on B lymphocyte development is unknown. The production of B lymphocytes in the bone marrow of CBA/N mice has now been compared with that of normal CBA/J mice by using two in vivo assays: immunofluorescence stathmokinetic studies measured pre-B cell proliferation, whereas radioautographic [3H]thymidine labeling was used to evaluate small lymphocyte turnover. Although the total cellularity of CBA/N mouse bone marrow was greater than normal, the absolute number of marrow small lymphocytes, pre-B cells, and B lymphocytes were all similar to those in CBA/J controls. Furthermore, in the bone marrow of CBA/N mice, the proliferation rate of pre-B cells, calculated from their rate of entry into mitosis, and the turnover rate of small lymphocytes, derived from their rate of [3H]thymidine labeling, were not significantly different from those seen in nondefective mice. The present findings that pre-B cell proliferation and small lymphocyte production proceed at similar rates in the bone marrow of xid and normal mice suggest that the xid gene does not act at the level of primary B cell genesis in the bone marrow. The findings are in accord with the view that the xid gene produces a maturation block or a functional abnormality among B lymphocytes in the peripheral lymphoid tissues rather than the deletion of a sublineage of B lymphocytes in the bone marrow.

B lymphocyte production in the bone marrow of mice with X-linked immunodeficiency (xid)

CBA/N mice carry an X-linked recessive immunodeficiency (xid) gene manifested by the absence of a B lymphocyte subpopulation, but the manner in which the xid gene exerts its effect on B lymphocyte development is unknown. The production of B lymphocytes in the bone marrow of CBA/N mice has now been compared with that of normal CBA/J mice by using two in vivo assays: immunofluorescence stathmokinetic studies measured pre-B cell proliferation, whereas radioautographic [3H]thymidine labeling was used to evaluate small lymphocyte turnover. Although the total cellularity of CBA/N mouse bone marrow was greater than normal, the absolute number of marrow small lymphocytes, pre-B cells, and B lymphocytes were all similar to those in CBA/J controls. Furthermore, in the bone marrow of CBA/N mice, the proliferation rate of pre-B cells, calculated from their rate of entry into mitosis, and the turnover rate of small lymphocytes, derived from their rate of [3H]thymidine labeling, were not significantly different from those seen in nondefective mice. The present findings that pre-B cell proliferation and small lymphocyte production proceed at similar rates in the bone marrow of xid and normal mice suggest that the xid gene does not act at the level of primary B cell genesis in the bone marrow. The findings are in accord with the view that the xid gene produces a maturation block or a functional abnormality among B lymphocytes in the peripheral lymphoid tissues rather than the deletion of a sublineage of B lymphocytes in the bone marrow.

Regulation of B-lymphocyte production in the bone marrow: role of macrophages and the spleen in mediating responses to exogenous agents

B-Lymphocyte production in mouse bone marrow can be stimulated by administering a variety of foreign materials in vivo. The nature and location of cells mediating this effect have now been studied, using assays of lymphocyte renewal and pre-B-cell proliferation. Pretreatment of mice with silica, to depress macrophage function, abolished the stimulation of small lymphocyte renewal produced by administering either sheep red blood cells (SRBC) or mineral oil and reduced the response to bovine serum albumin. The response was still abolished when silica was given 6 or 24 hr, but not 48 hr, after SRBC. Splenectomy prevented the stimulation of marrow lymphocyte renewal when performed either 4 weeks before or up to 72 hr after SRBC injection. The stimulation of pre-B-cell proliferation was similarly prevented by pretreatment with either silica or splenectomy. The results indicate that the wave of increased B-lymphocyte production after SRBC injection depends for the first 2-3 days upon silica-sensitive, spleen-dependent mechanisms, suggesting an early mediation by splenic macrophages. Primary B-lymphocyte production in vivo may thus normally be stimulated by exposure to external environmental agents acting indirectly on bone marrow B-cell progenitors via cellular reactions in peripheral lymphoid tissues.

The ontogeny and organization of the lymphoid system

The organization of the lymphoid system reflects 2 phases in the development and function of its component lymphocytes; a primary continuous genesis of 2 lineages of lymphocytes, B and T cells, is followed by a secondary wave of cell production and differentiation dependent on antigenic stimulation. Primary B cell genesis occurs multifocally before birth and in the bone marrow thereafter. Early progenitor cells give rise to proliferating pre-B cells containing free cytoplasmic mu chains, and thus to small lymphocytes expressing surface immunoglobulins, IgM, and IgD. Somatic rearrangement of genes in precursor cells produces clones of B cells, each member having an identical antigen-binding specificity. Primary T cell genesis occurs in the thymus, where an epithelial cell environment induces stem cells entering from embryonic mesoderm and postnatal bone marrow to proliferate extensively and to differentiate in discrete anatomical locations into 2 main sublineages, distinguishable by surface membrane markers. Primary B and T cells migrate rapidly to the spleen, lymph nodes, and mucosal lymphoid tissues where they may either die or be activated by antigens presented on macrophages and dendritic cells. Proliferation of activated B cells produces expanded clones of antigen-specific B memory cells in transient germinal centers. The secondary wave of B and T cells enters a pool of long-lived lymphocytes, which recirculate repeatedly between the blood and lymphoid organs, showing characteristic kinetics, migratory routes, and tissue localization. The entry of antigens accelerates local lymphocyte traffic and the retention of antigen-specific cells to promote an effective immune response. Despite important advances, many challenges remain in understanding the early differentiation, microenvironmental organization, and regulation of lymphoid cell populations in vivo.

Regulation of pre-B cell proliferation in bone marrow: immunofluorescence stathmokinetic studies of cytoplasmic mu chain-bearing cells in anti-IgM-treated mice, hematologically deficient mutant mice and mice given sheep red blood cells

To identify factors influencing the in vivo proliferate activity of bone marrow pre-B cells, the metaphase-blocking drug, vincristine sulfate, was injected into (a) mice depleted of B lymphocytes by treatment with anti-mouse IgM antibodies from birth; (b) hematologically deficient W/Wv and Sl/Sld mutants, and (c) mice injected with a foreign agent, sheep red blood cells (SRBC). Subsequently, a quantitative measure of pre-B cell proliferation was provided by examining marrow cells by immunofluorescence labeling for the absolute number of pre-B cells, identified by the presence of cytoplasmic mu chains (c mu) without surface mu (s mu), which had been arrested in metaphase. In anti-IgM-treated mice, some changes were observed in the size of the large pre-B cell population and in the incidence of mitotic cells after vincristine administration, but the overall production rate of pre-B cells did not differ from that in controls given normal rabbit serum. Pre-B cell kinetics in W/Wv and Sl/Sld mice also generally resembled those in homozygous controls. In contrast, after SRBC injection, there was an increase in the rate at which large pre-B cells entered mitosis. Thus, the proliferation of c mu + s mu- bone marrow pre-B cells shows no evidence of feedback control from the mature B lymphocyte pool, as indicated by lack of stimulation of pre-B cell production in anti-IgM-treated mice, and is independent of the hemopoietic defects of W/Wv or Sl/Sld mutants. On the other hand, the increased bone marrow pre-B cell proliferation after SRBC injection demonstrates that the magnitude of B cell genesis in the bone marrow can be influenced by extrinsic agents and thus may be influenced by environmental stimuli.

In vivo regulation of B lymphocyte production in the bone marrow: effects and mechanism of action of exogenous stimuli on pre-B cell proliferation and lymphocyte turnover

The present studies demonstrate that a single administration of an extrinsic agent (SRBC) can stimulate increased production of B lymphocytes in mouse bone marrow as revealed by 2 in vivo assays which quantitate pre-B cell proliferation and small lymphocyte renewal, respectively. The mechanisms mediating this stimulatory effect are sensitive to silica in vivo and require the presence of the spleen. Early events are both silica-sensitive and spleen-dependent, while a subsequent stage appears still to be spleen-dependent but not silica-sensitive. Sustained exogenous stimulation by multiple SRBC injections for 4 wk in young mice produces an expanded population size and increased production of pre-B cells and B lymphocytes in the bone marrow, apparently an elevated kinetic steady state of B lymphocyte production. (Formula: see text). As depicted schematically in Figure 1, the results suggest that the magnitude of bone marrow B lymphocyte production in vivo may reflect a basal level, putatively regulated by microenvironmental and other endogenous factors, which is amplified by exogenous environmental stimuli mediated by the action of macrophages located in the spleen. Further questions about such an environmental amplification (Fig. 1) concern the nature of later events in the spleen, the identity of putative stimulatory factors or cells circulating from the spleen to the bone marrow, the receptive target cell stages in the bone marrow and the consequences of this process with respect to the size and diversity of B lymphocyte clones and of primary humoral immune responses in vivo.

The localization of B lymphocytes in mouse bone marrow: radioautographic studies after in vivo perfusion of radiolabelled anti-IgM antibody

An in vivo cell surface labelling technique using radioautography has been developed to visualise the distribution of IgM-bearing B lymphocytes within the bone marrow. Anaesthetized 3-week-old mice were perfused via the common iliac artery with: (1) serum-containing medium (SCM), (2) 125I-labelled anti-IgM antibody in SCM, (3) SCM, and (4) fixative. In radioautographic sections of femoral marrow labelled surface IgM+ cells were observed either singly or in small clusters throughout the extravascular haemopoietic marrow cords. Binding specificity was demonstrated by the displacement of 125I-anti-IgM labelling by excess anti-IgM and by the binding of perfused 125I-anti-H-2Kk antibody in CBA/J (H-2Kk) mice but not in C57BL/6 (H-2Kb) mice. Quantitative analysis of radioautographic sections revealed an even distribution of labelled cells throughout CBA/J marrow perfused with 125I-anti-H-2Kk, indicating a uniform accessibility of perfused antibody to cells in the haemopoietic cords. This labelling pattern contrasted with that in 125I-anti-IgM perfused animals in which surface IgM+ cells, although widely distributed in the bone marrow, showed areas of concentration, speculatively clones of maturing B lymphocytes. This method of labelling surface IgM and other cell markers in situ provides an approach to study the microenvironment of B lymphocyte genesis in the bone marrow.

Heterogeneity of bone marrow lymphocytes: radioautographic detection of pre-B cells bearing cytoplasmic mu chains, and of B and T lymphocytes, and characterization of null lymphoid cells

A radioautographic immunolabeling technique has been developed to detect pre-B cells bearing cytoplasmic mu chains among populations of bone marrow lymphoid cells identified by conventional hematologic stains. 125I-Anti-mu antibody was applied either to fixed marrow smears, labeling total mu chains both in the cytoplasm (c mu) and at the cell surface (s mu), or to cell suspensions, labeling s mu alone. In stained radioautographs the incidence of c mu+ s mu- pre-B cells was derived both indirectly by subtracting values for s mu+ cells from those for total mu+ cells of various sizes in normal mice and directly by the total mu chain labeling in mice depleted of s mu+ cells by anti-IgM treatment in vivo. Binding specificity was demonstrated by the displacement of labeling by nonradioactive anti-mu antibody. The c mu+ s mu- cells showed a bimodal size distribution. They accounted for 40% of the large lymphoid cells and 30% of the small lymphocytes in the marrow. A further 50% of the small lymphocytes were B lymphocytes (s mu+) and 8% were T lymphocytes (Thy 1.2+). Thus, the technique demonstrates the presence of c mu+ s mu- pre-B cells among both proliferating large lymphoid cells and nondividing small lymphocytes, as classically defined in marrow smears. In addition, the results reveal a broad size distribution of mu- lymphoid cells, including a subset of small lymphocytes which lack c mu, s mu, and Thy 1.2 and thus cannot be assigned to either B or T lineage by these criteria. The findings suggest that in addition to B cells the marrow may produce other types of lymphoid cells, yet to be defined.

Genesis of B lymphocytes in the bone marrow: extravascular and intravascular localization of surface IgM-bearing cells in mouse bone marrow detected by electron-microscope radioautography after in vivo perfusion of 125I anti-IgM antibody

The role of mammalian bone marrow in generating surface IgM (sIgM)-bearing B lymphocytes is reviewed. Precursor cells in the marrow give rise to large, rapidly dividing cells bearing free cytoplasmic mu chains (c mu). The progeny of the large c mu+ cells form a population of small, nondividing c mu+ cells that mature into small lymphocytes, progressively expressing sIgM and other B-cell surface membrane components. Newly formed sIgM+ cells soon migrate through the bloodstream to the spleen and other lymphoid tissues, where they may die after a short lifespan or be activated to produce antibody molecules. The large-scale lymphocytopoiesis in the bone marrow thus maintains a population of rapidly renewed virgin B lymphocytes in the peripheral lymphoid tissues. This process continuously creates and selects B cell clones with the wide range of antibody specificities necessary to mediate primary humoral immune responses through postnatal life. A technique for perfusing radiolabeled anti-IgM antibodies in young mice has now permitted sIgM+ cells to be detected radioautographically in histological preparations of bone marrow under the electron microscope. Small sIgM+ lymphocytes are situated either singly or in small groups throughout the extravascular hemopoietic compartment of the bone marrow, often near sinusoid walls adjacent to late erythroblasts and reticular cells. Some regional concentrations of sIgM+ cells are apparent. sIgM+ cells also appear in transit through the sinusoidal endothelium and are markedly concentrated in the lumen of some sinusoids. Intrasinusoidal sIgM+ small lymphocytes have high densities of sIgM and long microvilli, on which sIgM molecules are concentrated. These studies reveal the localization and cell associations of specifically identified sIgM+ small lymphocytes in the extravascular marrow compartment and suggest that these cells may also undergo a transient intravascular storage and maturation phase. Use of this in vivo immunolabeling technique to detect other cell-surface markers may further elucidate the microenvironmental basis of B lymphocyte genesis in the bone marrow.

Pre-B cells in mouse bone marrow: in vitro maturation of peanut agglutinin binding B lymphocyte precursors separated from bone marrow by fluorescence-activated cell sorting

Peanut agglutinin (PNA) binding by mouse bone marrow cells and fractionation by the fluorescence-activated cell sorter have previously been shown to separate high concentrations of pre-B cells, as identified by cytoplasmic mu-chains (c mu). PNA+ and PNA- marrow cell fractions have now been assayed for the presence of functional pre-B cells able to generate mature B cells in culture, as defined by three criteria, the appearance of cell surface mu-chains (s mu), immunoglobulin secretion in response to bacterial lipopolysaccharides, and B cell colony formation. Small PNA+ cell fractions contained pre-B cells that developed into mature B lymphocytes in 1/2 to 1 day but did not sustain B cell production. Large PNA+ cells included pre-B cells that gave rise to mature B lymphocytes after an interval of 1 1/2 to 3 days and were able to sustain B cell genesis in vitro for at least 3 to 5 days thereafter. PNA- cell fractions contained mature B cells but lacked pre-B cell activity. The results demonstrate that PNA binding allows the separation of functional subsets of pre-B cells from bone marrow and that the three in vitro assays used in this study are closely comparable with one another as functional pre-B cell criteria. The findings suggest correlations between functional assays, c mu expression, PNA receptors, and cell size in characterizing stages of pre-B cell development.

Pre-B cells in mouse bone marrow: in vitro maturation of peanut agglutinin binding B lymphocyte precursors separated from bone marrow by fluorescence-activated cell sorting

Peanut agglutinin (PNA) binding by mouse bone marrow cells and fractionation by the fluorescence-activated cell sorter have previously been shown to separate high concentrations of pre-B cells, as identified by cytoplasmic mu-chains (c mu). PNA+ and PNA- marrow cell fractions have now been assayed for the presence of functional pre-B cells able to generate mature B cells in culture, as defined by three criteria, the appearance of cell surface mu-chains (s mu), immunoglobulin secretion in response to bacterial lipopolysaccharides, and B cell colony formation. Small PNA+ cell fractions contained pre-B cells that developed into mature B lymphocytes in 1/2 to 1 day but did not sustain B cell production. Large PNA+ cells included pre-B cells that gave rise to mature B lymphocytes after an interval of 1 1/2 to 3 days and were able to sustain B cell genesis in vitro for at least 3 to 5 days thereafter. PNA- cell fractions contained mature B cells but lacked pre-B cell activity. The results demonstrate that PNA binding allows the separation of functional subsets of pre-B cells from bone marrow and that the three in vitro assays used in this study are closely comparable with one another as functional pre-B cell criteria. The findings suggest correlations between functional assays, c mu expression, PNA receptors, and cell size in characterizing stages of pre-B cell development.

Pre-B cells in bone marrow: peanut agglutinin binding and separation of cytoplasmic mu chain-bearing cell populations in normal, post-irradiation and polycythemic mice using fluorescence-activated cell sorting

Mouse bone marrow cells exposed to fluorescein-conjugated peanut agglutinin (PNA) showed subsets of highly labeled cells when analyzed in a fluorescence-activated cell sorter. After separating three cell fractions of large and small PNA-binding cells and PNA-nonbinding cells, respectively, the B lymphocyte precursor (pre-B) cells, having cytoplasmic mu chains (c mu) without surface mu chains (s mu), were recovered solely in the PNA-binding fractions. Only a minority of s mu+ small lymphocytes having the lowest densities of s mu bound PNA. Small and large c mu+ s mu- pre-B cell populations were separated in high degrees of purity in the PNA-binding fractions, especially when obtained from bone marrow undergoing lymphoid regeneration after sublethal X-irradiation and during stimulation of lymphocyte production in post-polycythemic erythroid suppression. Characteristic shifts in the size distribution profile of PNA-binding cells reflected changes in the maturation stage of the pre-B cells. The results demonstrate that surface membrane components with strong PNA-binding capacities characterize c mu+ s mu- pre-B cells in the bone marrow during both normal and perturbed primary B lymphocyte genesis. The PNA-binding sites become undetectable soon after the first expression of s mu. This property permits the isolation from the bone marrow of high concentrations of subsets of large and small c mu+ s mu- cells in a viable state suitable for use in further functional studies.

Pre-B cells in bone marrow: size distribution profile, proliferative capacity and peanut agglutinin binding of cytoplasmic mu chain-bearing cell populations in normal and regenerating bone marrow

Pre-B cell populations in mouse bone marrow, identified by double immunofluorescence labelling of cytoplasmic and surface mu chains (c mu, s mu), have been characterized by cell size, proliferative capacity and the binding of peanut agglutinin (PNA). In the normal steady state of lymphocyte production the size distribution profile of cytocentrifuged c mu + s mu- cells was bimodal. A population of large cells in rapid cell cycle was revealed by arresting cells in mitosis with vincristine. Many c mu + s mu- cells, however, formed a nondividing population of small lymphocytes, resembling s mu + cells in size distribution. During regeneration from sublethal whole body X-irradiation (150 rads) a marked enrichment of large c mu + s mu- cells preceded small c mu + s mu- and s mu + cells; progressive changes in cell size distribution reflected a wave of B lymphocyte genesis. The c mu + s mu- cells in foetal liver resembled those in regenerating marrow. Surface binding of PNA characterised all c mu + s mu- cell populations in normal and regenerating bone marrow and in foetal liver, whereas only a minority of s mu + cells and mu-negative marrow cells bound PNA strongly. The present size distribution analyses allow a correlation with other cytological and functional studies of marrow lymphocyte precursors in defining the place of pre-B cells in B lymphocyte genesis.

Pre-B cells in mouse bone marrow: immunofluorescence stathmokinetic studies of the proliferation of cytoplasmic mu-chain-bearing cells in normal mice

By using a technique that combines metaphase arrest with immunofluorescence labeling, the proliferation of specifically identified pre-B cells in mouse bone marrow has been analyzed under physiological conditions in vivo. Pre-B cells bearing cytoplasmic mu-chains and no surface mu-chains constituted 12% of marrow nucleated cells, or 27 X 10(5) cells/femur, whereas surface mu-bearing B lymphocytes totaled 33 X 10(5) cells/femur. Pre-B cells measured 7 to 14 micron in diameter, the small number seen in metaphase (1 to 2%) being large cells (greater than 10 microns). After vincristine injection, the metaphase incidence (Imet) of pre-B cells increased with cell size; a broad-dose range of vincristine gave similar Imet values. Mitoses were arrested for 4 hr with no apparent cell death. Linear regression analysis of the increase in Imet of pre-B cells 2 to 4 hr after vincristine revealed a rate of entry into mitosis of 6.3%/hr, relative to all pre-B cells (average compartment turnover time, 16 hr), and 15.3%/hr for the large proliferating pre-B cell subset. This represented a pre-B cell production of 1.3 X 10(5) cells/femoral shaft/hr or 0.5 X 10(8) cells/whole bone marrow organ/day, emphasizing the magnitude of B lymphocyte genesis in normal bone marrow. Combined with reported renewal rates for small pre-B cells and small B lymphocytes, these values form a kinetic model of B lymphocyte development. The results reveal an apparent overproduction of large pre-B cells, consistent with a speculative post-mitotic loss of some immature primary B lymphocytes.

Pre-B cells in mouse bone marrow: immunofluorescence stathmokinetic studies of the proliferation of cytoplasmic mu-chain-bearing cells in normal mice

By using a technique that combines metaphase arrest with immunofluorescence labeling, the proliferation of specifically identified pre-B cells in mouse bone marrow has been analyzed under physiological conditions in vivo. Pre-B cells bearing cytoplasmic mu-chains and no surface mu-chains constituted 12% of marrow nucleated cells, or 27 X 10(5) cells/femur, whereas surface mu-bearing B lymphocytes totaled 33 X 10(5) cells/femur. Pre-B cells measured 7 to 14 micron in diameter, the small number seen in metaphase (1 to 2%) being large cells (greater than 10 microns). After vincristine injection, the metaphase incidence (Imet) of pre-B cells increased with cell size; a broad-dose range of vincristine gave similar Imet values. Mitoses were arrested for 4 hr with no apparent cell death. Linear regression analysis of the increase in Imet of pre-B cells 2 to 4 hr after vincristine revealed a rate of entry into mitosis of 6.3%/hr, relative to all pre-B cells (average compartment turnover time, 16 hr), and 15.3%/hr for the large proliferating pre-B cell subset. This represented a pre-B cell production of 1.3 X 10(5) cells/femoral shaft/hr or 0.5 X 10(8) cells/whole bone marrow organ/day, emphasizing the magnitude of B lymphocyte genesis in normal bone marrow. Combined with reported renewal rates for small pre-B cells and small B lymphocytes, these values form a kinetic model of B lymphocyte development. The results reveal an apparent overproduction of large pre-B cells, consistent with a speculative post-mitotic loss of some immature primary B lymphocytes.

Regulation of lymphocyte production in the bone marrow. I. Turnover of small lymphocytes in mice depleted of B lymphocytes by treatment with anti-IgM antibodies

To examine the concept that the genesis of lymphocytes in the bone marrow may be regulated by homeostatic feedback signals from peripheral B lymphocytes or their products, lymphocyte production was measured in mice selectively depleted of B lymphocytes by repeated administration of anti-IgM antibodies from birth. The turnover of small lymphocytes was quantitated radioautographically after DNA labeling by continuous infusion of 3H-thymidine. In the femoral marrow of anti-IgM-treated mice, the number of small lymphocytes was reduced and their turnover time was shorter than in control mice, presumably reflecting the premature elimination from the marrow of maturing cells about to express surface IgM. The absolute number of small lymphocytes being produced per femur in unit time, however, was identical in anti-IgM-treated and control mice. Lymphocyte production in the thymus was also unaffected by anti-IgM suppression whereas in the spleen the turnover of small lymphocytes was reduced due to the lack of young immigrant B lymphocytes from the bone marrow. The results demonstrate that the normal large-scale production of lymphocytes in mouse bone marrow is independent of the magnitude of the peripheral pool of B lymphocytes or the level of circulating immunoglobulins, suggesting the process is not subject to feedback control. Some implications for the genesis and diversity of primary B lymphocytes are discussed.

Regulation of lymphocyte production in the bone marrow. I. Turnover of small lymphocytes in mice depleted of B lymphocytes by treatment with anti-IgM antibodies

To examine the concept that the genesis of lymphocytes in the bone marrow may be regulated by homeostatic feedback signals from peripheral B lymphocytes or their products, lymphocyte production was measured in mice selectively depleted of B lymphocytes by repeated administration of anti-IgM antibodies from birth. The turnover of small lymphocytes was quantitated radioautographically after DNA labeling by continuous infusion of 3H-thymidine. In the femoral marrow of anti-IgM-treated mice, the number of small lymphocytes was reduced and their turnover time was shorter than in control mice, presumably reflecting the premature elimination from the marrow of maturing cells about to express surface IgM. The absolute number of small lymphocytes being produced per femur in unit time, however, was identical in anti-IgM-treated and control mice. Lymphocyte production in the thymus was also unaffected by anti-IgM suppression whereas in the spleen the turnover of small lymphocytes was reduced due to the lack of young immigrant B lymphocytes from the bone marrow. The results demonstrate that the normal large-scale production of lymphocytes in mouse bone marrow is independent of the magnitude of the peripheral pool of B lymphocytes or the level of circulating immunoglobulins, suggesting the process is not subject to feedback control. Some implications for the genesis and diversity of primary B lymphocytes are discussed.

Regulation of bone marrow lymphocyte production. IV. Cells mediating the stimulation of marrow lymphocyte production by sheep red blood cells: studies in anti-IgM-suppressed mice, athymic mice, and silica-treated mice

Some cellular requirements have been examined for the stimulation of lymphocyte production in mouse bone marrow by injected sheep red blood cells (SRBC). The increased genesis of marrow lymphocytes after a single dose of SRBC assayed radioautographically after [3H]thymidine labeling was unimpaired in the marrow of mice treated with anti-IgM antibodies from birth to eliminate B lymphocytes, and in congenitally athymic mice lacking T lymphocytes. However, pretreatment of mice with silica to depress macrophage function completely abolished the SRBC effect both on the total lymphocyte production and on the number of B and null small lymphocytes in the marrow. Comparative studies were performed on the thymus and spleen. The results demonstrate that the stimulation of marrow lymphocytes production by SRBC is mediated by a silica-sensitive mechanism, does not require B or T lymphocytes, and is independent of the humoral immune response. Thus, extrinsic agents may amplify the production of primary B cells and other lymphocytes in the bone marrow by an antigen-nonspecific mechanism, putatively mediated by macrophages.

Regulation of bone marrow lymphocyte production. III. Increased production of B and non-B lymphocytes after administering systemic antigens

To examine the influence of exogenous stimuli on the genesis of lymphocytes in mouse bone marrow, the production rate and subsets of marrow lymphocytes were examined after a systemic injection of sheep red blood cells (SRBC). Radioautographic analysis after either pulse labeling or infusion of [3H]thymidine revealed a pronounced increase in the number of newly formed small lymphocytes appearing in the marrow, maximal 4-5 days after SRBC injection and dose related. The resulting expansion of the marrow lymphocyte population included both immature B cells and null cells, as shown by cell surface and cytoplasmic markers. Similar stimulation of marrow lymphocyte production followed an injection of either bovine serum albumin or mineral oil. No comparable stimulation occurred in either the thymus or the spleen. The results demonstrate that antigens and nonspecific irritants can exert a central effect in the bone marrow, producing a surge in the production of both primary B and non-B lymphocytes. The possible role of external stimulants in determining the normal rate of bone marrow lymphocyte production is discussed.