B-cell suppression of antibody response to sheep red blood cells in mice of high- and low-responding genotypes.

CBA and C57B1 mice (high and low responders to sheep red blood cells, respectively) were injected intravenously with syngeneic lymph node, marrow, spleen, or thymus cells together with sheep red blood cells (SRBC), and the production of antibody-forming cells (AFC) was assayed in the spleen. Transfer of lymph node, marrow, spleen, or thymus cells led to a significant enhancement of immune responsiveness in low-responding C57B1 mice. In contrast, transfer of marrow, lymph node, or spleen cells to high-responding CBA mice was accompanied by a decline in AFC production. These effects were magnified if syngeneic cell donors had been primed with SRBC; suppression in CBA mice and stimulation in C57B1 mice were especially pronounced after transfer of SRBC-primed lymphoid cells. Pretreatment of CBA donors with cyclophosphamide in a dose causing selective B-cell depletion completely abrogated the suppression of immune responsiveness. A large dose (10⁷) of syngeneic B cells injected together with SRBC suppressed the accumulation of AFC in both CBA and C57B1 mice. No suppression of immune responsiveness was observed after transfer of intact thymus cells, hydrocortisone-resistant thymocytes, or activated T cells. We conclude that suppression of the immune response to SRBC is induced by B cells. At the same time, there is a possibility that the addition of “excess” B cells acts as a signal, triggering suppressor T cells.     

Effect of erythrocyte breakdown products on mast cells and erythropoietin formation]

Experiments were conducted on CBA mice and albino rats. A study was made of the effect of erythrocyte destruction products (EDP) on the content of hemopoietic colony-forming units (CFU), differentiation of stem cells and the erythropoietin production. It was shown that 3 or 4 EDP injections to normal mice or to lethally irradiated (1000 rad) mice after the transplantation of bone marrow cells caused no changes in the CFU level of stem cells differentiation. In case of a daily (for 3 days) administration of EDP to mice before the irradiation (1000 rad) and bone marrow transplantation there was observed an increase of the colonies count in the recipients' spleen on account of the erythroid colonies. EDP injection caused no changes in the erythropoietic activity of the blood serum. A possible role of erythrocyte destruction products in the mechanism of erythropoiesis autoregulation is discussed.     

Difference in genesis between antigen-induced IgM antibody-forming cells and B-cell mitogen-induced IgM antibody-forming cells in mouse spleen cell cultures.

To determine the mechanisms in the triggering of thymus-independent lymphocytes (B cells) for development into antibody-forming cells (AFC), genesis of IgM AFC elicited polyclonally by nonspecific stimulation with B-cell mitogen, such as nystatin and bacterial lipopolysaccharide, was compared with that of IgM AFC specifically elicited by antigenic stimulation, using mouse spleen cell cultures as an experimental system and sheep erythrocytes (SRBC) as a test antigen. Considering that differentiation and proliferation are necessary cellular events for precursor B cells to develop into AFC, the effect of different antimetabolic agents on the generation of each type of AFC in spleen cell cultures was examined. The generation of anti-SRBC IgM hemolysin plaque-forming cells (PFC) in B-cell mitogen-stimulated spleen cell cultures was found to be less susceptible to X-irradiation or mitomycin C than that in the SRBC-stimulated cultures. These apparently paradoxical results were affiirmed using colcemid as an inhibitor of cell mitosis and hydroxyurea (HU) as an inhibitor of cellular DNA synthesis. Thus, when spleen cell cultures responding to either SRBC or B-cell mitogen were exposed to colcemid or HU during a period from 2 days to 3 days after the stimulation, the exponential generation of anti-SRBC IgM PFC in the cultures responding to SRBC was completely halted, whereas that in the cultures responding to B-cell mitogen was not. Furthermore, N⁶, O^2′ -dibutyryl adenosine 3′, 5′ -cyclic monophosphoric acid was found to halt the exponential generation of antigen-induced anti-SRBC IgM PFC but not that of the B-cell mitogen-induced anti-SRBC IgM PFC. From these results it was suggested that B-cell mitogen might stimulate precursor Bμ cells at a late stage in the differentiative pathway to develop into AFC without cell division, and that antigenic stimulation might stimulate relatively primitive precursor Bμ cells to proliferate and then differentiate into AFC. Based on this idea, mechanisms in the triggering of B-cell activation are discussed.     

Effect of Trypanosoma brucei brucei on erythropoiesis in infected rats

Anemia generated from African trypanosome infection is considered an important symptom in humans and in domestic animals. In order to recover from anemia, the process of erythropoiesis is essential. Erythropoiesis is affected by erythropoietin (EPO), an erythropoietic hormone, supplying iron and inflammatory and proinflammatory cytokines. However, the role of these factors in erythropoiesis during African trypanosome infection remains unclear. In the present study, we analyze how erythropoiesis is altered in anemic Trypanosoma brucei brucei (interleukin-tat 1.4 strain [ILS])-infected rats. We report that the packed cell volume (PCV) of blood from ILS-infected rats was significantly lower 4 days after infection, whereas the number of reticulocytes, as an index of erythropoiesis, did not increase. The level of EPO mRNA in ILS-infected rats did not increase from the third day to the sixth day after infection, the same time that the PCV decreased. Kidney cells of uninfected rats cultured with ILS trypanosome strain for 8 hr in vitro decreased EPO mRNA levels. Treatment of both ILS and cobalt chloride mimicked hypoxia, which restrained the EPO-production-promoting effect of the cobalt. Messenger RNA levels of β-globin and transferrin receptor, as markers of erythropoiesis in the bone marrow, also decreased in ILS-infected rats. Levels of hepcidin mRNA, which controls the supply of iron to the marrow in liver, were increased in ILS-infected rats; however, the concentration of serum iron did not change. Furthermore, mRNA levels of interleukin-12, interferon-γ, tumor necrosis factor-α, and macrophage migration inhibitory factor in the spleen, factors that have the potential to restrain erythropoiesis in bone marrow, were elevated in the ILS-infected rats. These results suggest that ILS infection in rats affect erythropoiesis, which responds by decreasing EPO production and restraining its function in the bone marrow.     

Different effect of testosterone on polypotential stem hematopoietic stem cells and immunocompetent B-lymphocytes]

A research was made to study the dynamics of the proliferative, colony-forming and migration capacity of stem hemopoietic cells in (CBA X C57Bl) F1 hybrid mice under the influence of testosterone propionate, 10 mg/100 g, as well as the migration of immunocompetent B lymphocytes from the bone marrow to the spleen and the accumlation of their progeny, antibody-producing cells, in the spleen. The immunodepressive effect of testosterone was manifested by a decrease in the migration of B cells and the number of antibody-producing cells in the spleen. On the contrary, testosterone had a stimulating effect on the functional activity of stem hemopoietic cells, increasing their proliferation and migration. Under conditions of the suppressed erythropoietic differentiation of multipotent stem hemopoietic cells the injection of testosterone resulted in an increase in the number of antibody-producing cells in the spleen. This suggests that the stimulation of erythropoiesis and immunosuppression, induced by testosterone, are interconnected and determined by the direct action of the hormone on the cellular cycle of the stem cells, as well as by their prevailing differentiation towards the erythroid series, resulting in the decrease of their differentiation into B cells.     

A mathematical model of erythropoiesis in mice and rats. Part 4: Differences between bone marrow and spleen

In a preceding analysis we hypothesized that the most important parameter controlled by erythropoietic regulation in vivo is the degree of amplification (number of cell divisions) in the CFU-E and erythroblast cell stages. It was concluded that erythropoietic amplification in vivo is controlled according to a sigmoidal dose-response relationship with respect to the control parameter which is the haematocrit (or haemoglobin concentration). Here, this hypothesis is extended to include the differences in murine bone marrow and splenic erythropoiesis that are described and quantified by different dose-response relationships. Comparing several sets of experimental data with mathematical model simulations, this approach leads to the following conclusions: (i) in the unperturbed normal steady state at least one extra erythropoietic cell division takes place in the spleen compared with the bone marrow; (ii) a strong erythropoietic stimulus, such as severe bleeding or hypoxia, can induce five to six additional cell divisions in the spleen but only two to three additional divisions in the bone marrow; this results in a considerable increase in the spleen's contribution to erythropoiesis from about 10% in normal animals to over 40% during strong stimulation; (iii) under erythropoietic suppression, such as red cell transfusion, a similar number of cell divisions is skipped in both organs and the splenic contribution to erythropoiesis remains unchanged. In conclusion, the concept that bone marrow and spleen microenvironments differ in the dose-response relationship for erythropoietic regulation provides an explanation for the changing contribution of splenic murine erythropoiesis following a variety of experimental treatments.     

A mathematical model of erythropoiesis in mice and rats. Part 4: Differences between bone marrow and spleen

Abstract. In a preceding analysis we hypothesized that the most important parameter controlled by erythropoietic regulation in vivo is the degree of amplification (number of cell divisions) in the CFU-E and erythroblast cell stages. It was concluded that erythropoetic amplification in vivo is controlled according to a sigmoidal dose-response relationship with respect to the control parameter which is the haematocrit (or haemoglobin concentration). Here, this hypothesis is extended to include the differences in murine bone marrow and splenic erythropoiesis that are described and quantified by different dose-response relationships. Comparing several sets of experimental data with mathematical model simulations, this approach leads to the following conclusions: (i) in the unperturbed normal steady state at least one extra erythropoietic cell division takes place in the spleen compared with the bone marrow; (ii) a strong erythropoietic stimulus, such as severe bleeding or hypoxia, can induce five to six additional cell divisions in the spleen but only two to three additional divisions in the bone marrow; this results in a considerable increase in the spleen's contribution to erythropoiesis from about 10% in normal animals to over 40% during strong stimulation; (iii) under erythropoietic suppression, such as red cell transfusion, a similar number of cell divisions is skipped in both organs and the splenic contribution to erythropoiesis remains unchanged. In conclusion, the concept that bone marrow and spleen microenvironments differ in the dose-response relationship for erythropoietic regulation provides an explanation for the changing contribution of splenic murine erythropoiesis following a variety of experimental treatments.     

Effects of cyclophosphamide on murine bone marrow and splenic megakaryocyte-CFC,granulocyte-macrophage-CFC,and peripheral blood cell levels

The effect of cyclophosphamide (CY) on megakaryocytopoiesis in mice was examined with assays of megakaryocyte colony-forming cells (Meg-CFC) in bone marrow and spleen and simultaneous determinations of peripheral blood counts, after a single intraperitoneal dose (200 mg/kg) of CY. Significant rebound thrombocytosis (170% of normal) occurred at day 11 after injection with CY, although only modest preceding thrombocytopenia (70% of normal) was observed. After an initial 3–5-day period of suppression, total megakaryocyte colony-forming cells (Meg-CFC) in both bone marrow and spleen of CY-treated mice demonstrated rebound increases at 5 and 7 days, respectively, after administration of the drug. Granulocyte-macrophage colony-forming cells (GM-CFC) exhibited alterations which were similar to those of Meg-CFC, suggesting similar sensitivities of Meg-CFC and GM-CFC to CY. The increase in Meg-CFC in both bone marrow and spleen preceded development of thrombocytosis by 4–6 days. This suggests that increased platelet counts in CY-treated mice are attributable, at least in part, to alterations in feedback mechanisms which control megakaryocytopoiesis, with resultant stimulation of the megakaryocyte progenitor compartment.     

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.     

The regenerating liver: a site of erythropoiesis in the adult Long-Evans rat

Erythropoiesis, which is primarily hepatic in the rat during fetal and early neonatal life, shifts almost entirely to the bone marrow in the neonatal-adolescent stage of development. In the adult, extramedullary erythropoiesis has been demonstrated in the liver and spleen under certain pathological conditions when bone marrow red cell production is insufficient. In the present study, erythropoietic foci have been found in young-adult rat liver regenerating 24-72 hr after subtotal hepatectomy. This erythropoiesis is both extravascular and sinusoidal, with some erythroblastic islands noted. The centrolobular hepatic area contains the highest concentration of erythroblasts. Peripheral blood reticulocytosis coincides with the appearance of these cells and this is considered as an indicator of effective erythropoiesis. Liver regenerating after partial hepatectomy produces significant quantities of erythropoietin (Ep) in response to hypoxia. Subtotal hepatectomy may confer upon the adult liver the ability to revert to a fetal-like condition both in its ability to produce Ep and to function as a hematopoietic inductive microenvironment for erythropoiesis.     

Studies on the mechanisms of action of BCG

Summary Bacillus Calmette-Guérin was given intravenously (i.v.) or subcutaneously (s.c.), 14 days before antigenic or mitogenic stimulation.When given i.v., BCG increased plaque-forming cell production against thymus-dependent antigens (sheep red blood cells and a hapten coupled to hemocyanin) and against a thymus-independent antigen (the same hapten coupled to polymerized flagellin). BCG given s.c. was generally ineffective in potentiating humoral responses.In contrast, a marked depression of spleen cell reactivity in vitro to a T-cell mitogen, concanavalin A (Con A) but an increased response to a B-cell mitogen, dextran sulfate, were observed after BCG i.v., and to a lesser extent after BCG s.c. This inhibitory effect was reversed after removal of cells adherent to nylon or plastic. Normal spleen cell reactivity to Con A was strongly depressed when the cells were cultivated in presence of unfractionated or plastic-adherent BCG-treated spleen cells, suggesting that BCG induces suppressor cells which inhibit T-cell responses in vitro. Similar impairment of T-cell functions in vivo was not observed since BCG given i.v. significantly increased the intensity of delayed-type hypersensitivity to picryl chloride.BCG also induced macrophage activation, measured by macrophage tumoricidal activity in vitro, more strongly and more rapidly when given i.v. than s.c.Modifications of the distribution of lymphocytes from the circulation to the organs were observed. An early increase of lymphocyte migration to the spleen and a long-lasting depression of cell migration to mesenteric lymph nodes and bone marrow were seen after BCG given i.v. When given s.c., BCG induced a progressive increase of cell migration to the draining lymph nodes concomitant with a depression of migration to mesenteric nodes.These results demonstrate the complexity of the mode of action of BCG, but many of its effects on immune responses may result from a primary action on macrophages.     

Histamine production by alloantigen-activated mouse bone marrow cells

Histamine's contribution to the manifestations associated with graft-versus-host disease (GVHD) and/or hybrid resistance is unknown. Thus, we initiated studies to see whether or not mouse bone marrow cells could produce histamine upon alloantigen stimulation. Irradiated allogeneic spleen cells were shown to stimulate bone marrow cells to produce and secrete high levels of histamine. During 7 days of culture there was only a marginal increase in cell-associated histamine while the amount of histamine in the supernatant increased 10- to 20-fold. Optimal histamine production was dependent upon Lyt 1+2+ T cells resident in the bone marrow. Further, bone marrow cells from Nude mice failed to produce high levels of histamine following alloantigen stimulation. Soluble factors produced by alloantigen-stimulated bone marrow cells or by Con A-stimulated rat spleen cells induced high levels of histamine production in bone marrow cells in the absence of alloantigen. We suggest that histamine production by alloantigen-activated bone marrow cells may modulate immune functions following bone marrow transplantation.     

In vitro production of CFU-S and cells with erythropoiesis repopulating ability by 5-fluorouracil treated mouse bone marrow

Mouse bone marrow, obtained from donors three days after treatment with 5-fluorouracil, had a very low ability to form macroscopic spleen colonies in irradiated mice at 10 days after transplantation of the cells (CFU-S10); such marrow also had no detectable erythropoiesis repopulating ability but did have near normal marrow repopulating ability and spleen megakaryocyte repopulating ability. Incubation of this marrow in vitro for 7 days with medium containing growth factor preparations (a) pregnant mouse uterus extract plus human spleen conditioned medium or (b) mouse spleen conditioned medium, resulted in marked increases in CFU-S10 and in cells with erythropoietic repopulating ability together with maintenance of cells with marrow repopulating ability. These responses were not observed in cultures with control medium alone. Spleen megakaryocyte repopulating ability was also maintained in the presence of the factor preparations.     

Mechanism of the adjuvant action: effect on the stem cell and B-lymphocyte migration from the bone marrow]

The authors studied the influence of synthetic polyelectrolytes of polyacrylic acid and poly-2-methyl-5-vinylpyridine and of complete Freund's adjuvant on the migration of stem cells and B-lymphocytes from mouse bone marrow. The stem cell count was evaluated by the number of splenic colonies; as to B-cell migration--it was assessed by the accumulation of the antibody-forming cells forming from B-lymphocytes migrating in the spleen in the transfer of fixed number of T-lymphocytes. As revealed the synthetic substances under study intensified the migration of stem cells and of B-lymphocytes to a much greater extent than Freund's adjuvant. The mechanisms of the influence of the adjuvants used on cell migration processes are discussed.     

Effect of hydrocortisone and bacterial lipopolysaccharide on colony-stimulating activity production from mouse marrow adherent cells, spleen cells and peritoneal macrophages in vitro

The effect of hydrocortisone (HC) on colony-stimulating activity (CSA) production from mouse bone marrow adherent cells, spleen cells and peritoneal macrophages with or without bacterial lipopolysaccharide (LPS) stimulation was studied. CSA in the supernatant from bone marrow adherent cells incubated with HC was found to be five times higher than CSA from cultures without LPS stimulation. In contrast, the CSA production by spleen cells and peritoneal macrophages were significantly suppressed by HC in both LPS-stimulated and non-stimulated cultures. These studies suggest that the effect of HC on CSA production was quite different depending on the target cells.     

Erythropoiesis in murine long-term bone-marrow cell cultures: dependence on erythropoietin and endogenous production of an erythropoietic stimulating activity

Erythropoiesis was obtained in murine long-term bone-marrow cell cultures (LTBMCs) in the presence of erythropoietin (Epo) when the medium was frequently renewed. The level of the erythropoietic differentiation was shown to be a function of the erythropoietin concentration. In response to Epo addition, an activity which stimulates CFU-E proliferation in semisolid cultures of fresh bone marrow cells was detected in the LTBMC supernatants. These results suggest that another factor, whose synthesis may be under Epo control, participates in the stimulation of erythropoiesis in vitro.     

Mechanisms of the adjuvant effect of nystatin on in vitro antibody response of mouse spleen cells: indication of nystatin as a B-cell mitogen and as a stimulant for polyclonal antibody synthesis in B cells.

Adjuvanticity of nystatin, one of the polyenic antifungal antibiotics having as its primary target the membrane sterol of eukaryotic cells, was investigated by examining its effect on several functions of mouse spleen cells relevant to immunological phenomena in vitro. Nystatin was found to stimulate significantly DNA synthesis in thymus-independent (B) cells but not in thymus-dependent (T) cells. Like the other B-cell mitogens such as bacterial lipopolysaccharide (LPS), nystatin elicited nonspecifically polyclonal antibody synthesis in mouse spleen cell cultures, and also restored antibody response of T cell-deficient spleen cells of congenitally athymic nude mice to heterologous erythrocytes (RBC; thymus-dependent antigen). Thus, nystatin and LPS appeared to cause similar changes in the functions of spleen cells relevant to immunological events. However, antagonism but no additive effect in the adjuvanticity was revealed between the two adjuvants. As an interesting finding, the polyclonal generation of anti-RBC antibody-forming cells (AFC) in the spleen cell cultures by stimulation with B-cell mitogen, i.e., either nystatin or LPS, was not inhibited at all by inclusion of any anti-RBC antiserum, whereas, as is well known, the generation of AFC by stimulation with the antigen was specifically suppressed by the corresponding antiserum, indicating a difference in the genesis between the mitogen-induced AFC and the antigen-induced AFC.     

Effect of liposomal muramyl tripeptide phosphatidylethanolamine and indomethacin on hematopoietic recovery in irradiated mice

The effects of liposomal muramyl tripeptide phosphatidylethanolamine (MTP-PE/MLV, radioprotective immunomodulator; 10 mg/kg) and indomethacin (INDO, inhibitor of prostaglandin production; 2 mg/kg) on post-irradiation recovery of hematopoietic functions in mice were investigated. Two agents with distinct radioprotective mechanisms were administered alone or in combination 24 h and 3 h before exposure to 7 Gy (60)Co radiation. In the post-irradiation period (3-14 days) combined pre-treatment of mice accelerated recovery of bone marrow cellularity, weight of spleen and myelopoietic and erythropoietic activity in both hematopoietic organs, compared to treatment with MTP-PE/MLV or indomethacin alone. In the peripheral blood, improved radioprotective effects of combined drug administration were found in the recovery of reticulocytes and platelet count. No further significant differences in the recovery of leukocyte count were observed in the examined groups until post-irradiation day 14. Within the first 3-6 post-irradiation days, the bone marrow and peripheral blood smears of mice pre-treated with indomethacin alone or its combination with MTP-PE/MLV more frequently featured blast cells and large cells with abundant cytoplasm which could be considered the hematopoietic stem cells.     

Erythroid stem cells in Friend-virus infected mice

The erythropoietic stem cell compartment was studied in Friend-virus (polycythemic strain, FV-P) infected DBA/2 and NMRI mice with the CFUE and BFUE technique. Early after infection there was a depression in CFUE number in bone marrow and spleen, followed by an increase of the CFUE concentration, earlier and more pronounced in the spleen than in the marrow. Three days after FV-P infection an erythropoietin (Ep) independent CFUE population started to grow and replaced the normal Ep-dependent population within 8 to 12 days. The shift to Ep independency was not gradual. CFUE colonies of FV-P infected bone marrow cells were two to three times larger than control colonies after three days in vitro incubation. BFUE colonies increased in number during the first days of infection, but were totally lost after more than ten days. After velocity sedimentation of bone marrow cells of FV-P infected animals, however, the BFUE containing fractions showed normal BFUE colony growth and normal Ep sensitivity. In unfractionated bone marrow cell cultures BFUE colony growth could be observed later than ten days post infection when the cultures were refed with medium. It was therefore concluded that the loss of BFUE colony growth after FV-P infection was an in vitro artefact due to inadequate culture conditions.     

T cell regulation of interferon-alpha/beta (IFN-alpha/beta) production by alloantigen-stimulated bone marrow cells

We have previously reported that mouse bone marrow cells produce high levels of interferon-alpha/beta (IFN-alpha/beta) after 5 to 6 days of in vitro culture with irradiated allogenic spleen cells. The current study was initiated to determine whether or not T cells are important for alloantigen-induced IFN-alpha/beta production by mouse bone marrow cells. Bone marrow cells and spleen cells were obtained from C57BL/6 mice. These cells were treated with different monoclonal antisera and complement, and then were cultured 5 to 6 days with irradiated DBA spleen cells. The results from these experiments indicated that optimal IFN-alpha/beta production by alloantigen-stimulated bone marrow cells required Lyt-1+2+ T cells. In addition, when bone marrow cells obtained from nu/nu B10 mice were cultured with alloantigen, only low levels of IFN were produced when compared with IFN production by bone marrow cells obtained from normal littermate B10 mice. The addition of nylon wool-enriched splenic T cells to cultures containing bone marrow cells and alloantigen resulted in an augmentation of IFN-alpha/beta production by three-fold to fivefold. Furthermore, bone marrow cells obtained from alloantigen-immunized mice produced much higher levels of IFN-alpha/beta and in a shorter period of time (2 to 3 days) when compared with bone marrow cells obtained from control or non-immunized mice. Cyclosporin A (CsA) has been shown to inhibit predominantly T cell-dependent responses. The effect of CsA on IFN production by alloantigen-stimulated bone marrow and spleen cells was investigated. The addition of CsA at concentrations as low as 0.1 micrograms/ml inhibited not only IFN-gamma production by alloantigen-stimulated spleen cells, but also IFN-alpha/beta production by alloantigen-stimulated bone marrow cells. In contrast, IFN-alpha/beta production by Newcastle disease virus-infected spleen cells, bone marrow cells, or L cells was not inhibited by the addition of CsA (1 microgram/ml). Thus, the ability of bone marrow cells to produce high levels of IFN-alpha/beta after in vitro culture with alloantigen is dependent upon T cells resident in the bone marrow. IFN-alpha/beta production by alloantigen-stimulated bone marrow cells may play a major role in the pathogenesis associated with graft-vs-host disease and in T cell regulation of hematopoiesis.