Developmental regulation of granulocyte-macrophage colony-stimulating factor production during human monocyte-to-macrophage maturation

Summary Cells of the macrophage lineage are a major source of various cytokines and hematopoietic growth factors. With regard to the growth factors acting on cells of their own lineage, macrophage colony-stimulating factor (M-CSF) has been proven to be secreted by monocytes (MO) and macrophages (MAC), whereas the production of granulocyte-macrophage colony-stimulating factor (GM-CSF) by human MO/MAC is under debate. Here we report that in elutriation-purified MO, as well as in MAC derived from cultured MO, GM-CSF m-RNA was regularly induced by LPS. In MO the GM-CSF message was still detectable 18h after stimulation under serum-free conditions, but in contrast was already lost at this time point in MAC. Secreted GM-CSF protein was detected in the culture medium using a sandwich ELISA. Furthermore, a factor-dependent cell line (M-07) was used for a biological assay. Here, a neutralizing anti GM-CSF antibody specifically blocked the proliferation-inducing activity of MO/MAC supernatants. Whereas only small amounts of GM-CSF were detected in MO, its secretion increased severalfold upon MO-to-MAC differentation in vitro. A similar increase upon in vitro maturation of MO was observed for the production of granulocyte colony-stimulating factor. The highest amounts of GM-CSF (up to 2.8 ng/10⁶ cells) were produced by MAC that had been derived from MO cultured under serum-free conditions in the presence of 0.5 mg/ml albumin as the only medium supplement.This work was supported by theDeutsche Forschungsgemeinschaft (AN 111).     

Effects of Mycobacterium avium complex-infection treatment on cytokine expression in human immunodeficiency virus-infected persons: results of AIDS clinical trials group protocol 853

Human immunodeficiency virus (HIV) type 1-infected persons with newly diagnosed Mycobacterium avium complex (MAC) bacteremia were enrolled in an 8-week study to determine whether treatment of MAC infection is associated with decreases in plasma tumor necrosis factor (TNF)-alpha levels. Blood specimens were obtained for quantitative MAC cultures and to determine plasma levels of HIV RNA, TNF-alpha, and other proinflammatory cytokines. MAC levels decreased by 1.75 log at week 4 (P=.008) and by 2.48 log at week 8 (P=.001). Plasma TNF-alpha decreased by 0.15 log at week 4 (P=.042) and by 0. 40 log at week 8 (P=.027). Plasma interleukin (IL)-6 decreased by 0. 56 log at week 8 (P=.039). There were nonsignificant trends (P<.10) for plasma levels of IL-1beta and HIV RNA to decrease at week 8. Nonsignificant decreases in plasma levels of TNF-alpha, IL-1beta, IL-6, and HIV RNA were also seen in those individuals who remained on stable antiretroviral therapy throughout the 8 weeks of the study.     

Regulation of cytokine expression by interferon-alpha in human bone marrow stromal cells: inhibition of hematopoietic growth factors and induction of interleukin-1 receptor antagonist

We investigated the effects of interferon-alpha (IFN-alpha) on the expression of cytokines by human bone marrow stromal cells. Production of granulocyte-macrophage colony-stimulating factor (GM-CSF), granulocyte-CSF (G-CSF), and interleukin-1 beta (IL-1 beta) in stromal cell layers was induced by incubation with IL-1 alpha, tumor necrosis factor (TNF), or lipopolysaccharide (LPS). Addition of IFN-alpha to such stimulated cultures resulted in a strong downregulation of mRNA expression of GM-CSF and IL-1 beta. Similarly, the protein levels of GM- CSF and IL-1 beta were significantly reduced by IFN-alpha, whereas G- CSF production was only moderately inhibited. In contrast, IFN-alpha markedly stimulated the production of IL-1 receptor antagonist (IL-1RA) by stromal cells. The inhibition of cytokine expression resulted in a reduced hematopoietic activity of stromal cells, indicated by a reduced proliferation of the factor dependent cell line MO7e on IFN-alpha- treated stromal cells. In the presence of cycloheximide (CHX), IFN- alpha failed to inhibit IL-1 mRNA expression, whereas the regulation of GM-CSF and IL-1RA by IFN-alpha was not affected. Our results indicate that the myelosuppressive effects of IFN-alpha, as observed in therapeutic applications or associated with viral infections, are, in part, indirectly mediated by inhibition of the paracrine production of hematopoietic growth factors.     

Production of cytokines by peripheral blood monocytes/macrophages infected with human immunodeficiency virus type 1 (HIV-1)

The study of monocyte/macrophage functions after human immunodeficiency virus type 1 (HIV-1) infection may help in understanding the pathogenesis of AIDS. The production of four cytokines, tumor necrosis factor alpha (TNF alpha), interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6), and granulocyte-macrophage colony-stimulating factor (GM-CSF), by peripheral blood monocytes/macrophages was evaluated after in vitro infection with HIV-1. HIV-1 infection of these monocytes/macrophages did not result in release of any of these cytokines. Similarly, treatment of uninfected cells with purified recombinant HIV-1 envelope protein did not result in cytokine production. After stimulation with endotoxin or endotoxin plus interferon-gamma, HIV-1-infected monocytes/macrophages produced amounts of TNF alpha, IL-6, GM-CSF, and IL-1 beta comparable to that of uninfected cells. HIV-1 infection does not appear to induce or alter cytokine production by mononuclear phagocytes, which retain the capacity to produce these cytokines after endotoxin stimulation.     

Mycobacterium tuberculosis upregulates coreceptors CCR5 and CXCR4 while HIV modulates CD14 favoring concurrent infection

Tuberculosis is the most frequent coinfection in humans infected with HIV-1, but little is known about mechanisms that favors coinfection. The aim of this work is to understand tuberculosis and HIV infections. We determined the pattern of expression of CD11c, CD14, CD40, CCR5, and CXCR4 and quantified IL-1beta, IL-6, IL-8, TNF-alpha, and RANTES in tuberculosis patients and HIV patients. Monocytes from healthy PPD+ volunteers (HP(+)V) stimulated with intracellular proteins (IP), lipids, and polysaccharides (PLS) from Mycobacterium tuberculosis down regulate CD11c expression (p < 0.05). On the contrary, CD14 expression was elevated in tuberculosis patients (p < 0.05) and HIV-infected patients (p > 0.05). CD14 expression was elevated on monocytes from HP(+)V stimulated with PLS and lipids (p < 0.05). CD40 low expression was found in tuberculosis patients and on monocytes from HP(+)V stimulated with lipids, but it was elevated in HIV-infected patients (p < 0.05). CXCR4 and CCR5 expression was high in pulmonary tuberculosis patients and low in HIV-infected patients (p < 0.05). Finally, CCR5+ monocytes from HP(+)V after stimulation with PLS and CXCR4+ lymphocytes were elevated after stimulation with IP (p < 0.05). In general, high levels of IL-1beta, IL-6, and TNF-alpha were found in all groups, but low levels of RANTES were found in pulmonary tuberculosis patients. In conclusion, the pulmonary tuberculosis patients have a microenvironment that facilitates the HIV infection through three possible mechanisms: (1) increasing the coreceptor for HIV entrance, (2) increasing proinflammatory cytokines, and (3) down-regulating RANTES. At the same time, HIV patients have a microenvironment that facilitates entry of M. tuberculosis into macrophages through CD14.     

A soluble factor induced by an extract from Pinus parviflora Sieb et Zucc can inhibit the replication of human immunodeficiency virus in vitro.

We showed that an extract (PC6) from cones of Pinus parviflora Sieb et Zucc induced the human T-cell line CEM to produce a pepsin-sensitive soluble factor(s) that could inhibit the replication of the type 1 human immunodeficiency virus (HIV-1) in CEM T cells, in U-937 histocytes, in THP-1 monocytes, and in mitogen-activated human tonsillar mononuclear cells. Indirect immunofluorescence staining and polymerase chain reaction analysis of the PC6-induced CEM cells revealed the absence of known lymphokines/cytokines except granulocyte/macrophage colony-stimulating factor (GM-CSF), interleukin 3 (IL-3), transforming growth factor beta 1 (TGF-beta 1), and tumor necrosis factor alpha (TNF-alpha). However, functional studies with recombinant IL-3, TNF-alpha, and TGF-beta 1 showed that these three factors did not inhibit HIV-1 replication in CEM cells. Neutralization of the PC6-induced HIV-1-inhibiting factor(s) with commercially available neutralizing antibodies to GM-CSF and TNF-alpha also did not abrogate the anti-HIV-1 impact. Thus, the anti-HIV-1 factor induced by PC6 may be novel. Molecular sieve separation showed that the anti-HIV-1 factor(s) is smaller than 30 kDa. Affinity chromatography using a DEAE-cellulose column enriched the factor that inhibited HIV-1.     

Bacterial vaginosis, not HIV, is primarily responsible for increased vaginal concentrations of proinflammatory cytokines

The relative effect of HIV-1 infection compared with vaginal infections on vaginal cytokine concentrations is not well characterized. We compared vaginal fluid samples from HIV-1-infected women with those from HIV-negative women, to assess the effect of HIV-1 infection on concentrations of vaginal proinflammatory cytokines and the mucosal defense molecule secretory leukocyte protease inhibitor (SLPI). Twenty-seven HIV-1-infected women and 54 HIV-negative controls, matched for bacterial vaginosis (BV) status, had proinflammatory cytokine [interleukin (IL)-1beta, IL-6, IL-8] and SLPI concentrations measured from archived cervicovaginal lavage and vaginal swab samples using an enzyme-linked immunosorbent assay (ELISA). Log-transformed concentrations were compared by BV and HIV status in univariate analysis using Student's t-test, and in multivariate analysis using a linear regression model. In univariate analysis there were no significant differences in cytokine concentrations among HIV-1-infected and HIV-negative women. In a multivariable linear regression model, BV was significantly associated with an increase in IL-1 beta (p = 0.003). HIV infection was associated with an increased concentration of SLPI (p = 0.008), while BV status was significantly associated with a decrease in SLPI concentrations (p = 0.005). Neither HIV nor BV was associated with changes in IL-6 or IL-8. HIV does not have a major impact on vaginal concentrations of proinflammatory cytokines when controlling for the presence of bacterial vaginosis.     

Monoclonal antibody against the common beta subunit (beta c) of the human interleukin-3 (IL-3), IL-5, and granulocyte-macrophage colony-stimulating factor receptors shows upregulation of beta c by IL-1 and tumor necrosis factor-alpha.

High-affinity receptors for human granulocyte macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), and IL-5 are composed of two distinct subunits, alpha and beta. Each receptor has its own ligand-specific alpha subunit, and the three receptors share the common beta subunit, beta c. Using a transfectant of NIH3T3 cells expressing the high-affinity human GM-CSF receptor, monoclonal antibodies (MoAbs) against beta c were generated. These MoAbs specifically bound to cells bearing beta c and immunoprecipitated the beta c protein of 120 Kd. Using these MoAbs, expression of beta c was examined. It is known that IL-1 augments the proliferative response of a human factor-dependent hematopoietic cell line TF-1 to either GM-CSF, IL-3, or IL-5, and that it upregulates the high-affinity receptors for GM-CSF, IL-3, and IL-5. Antibody binding and immunoprecipitation demonstrated that IL-1 increased cell surface expression of beta c. This enhancement by IL-1 was accompanied by an increased level of beta c mRNA. In addition, we found that tumor necrosis factor-alpha (TNF-alpha) also increased the expression of beta c, although it did not augment the proliferative response of TF-1 to GM-CSF, IL-3, and IL-5.     

Interleukin-2-activated natural killer cells can support hematopoiesis in vitro and promote marrow engraftment in vivo.

Purified natural killer (NK) cells were obtained from mice with severe combined immune deficiency (SCID) to ascertain their effect on hematopoiesis. When activated and propagated with recombinant human interleukin-2 (rhIL-2) in vitro, SCID spleen cells maintained a phenotypic and lytic spectrum consistent with a pure population of activated NK cells. When added with syngeneic bone marrow cells (BMC) in soft agar, the activated NK cells could support hematopoietic growth in vitro without the addition of exogenous hematopoietic growth factors. However, when syngeneic BMC were added along with cytokines to produce optimal growth conditions, the addition of NK cells was then inhibitory for hematopoietic colony formation. Antibodies to interferon-gamma (IFN-gamma) partially reversed the inhibitory effects. Supernatants from the NK-cell cultures could also exert these effects on hematopoiesis, although to a lesser extent. Analysis of the NK cell RNA demonstrated that activated NK cells express genes for hematopoietic growth factors such as granulocyte-macrophage colony-stimulating factor (GM-CSF), granulocyte CSF (G-CSF), and IL-1 beta. The NK cells were also found to express IFN-gamma, transforming growth factor-beta 1 (TGF-beta 1), and tumor necrosis factor-alpha (TNF-alpha) mRNA. Analysis of the NK-cell supernatants using factor-dependent myeloid progenitor cell lines showed that the NK cells were producing G-CSF and growth-promoting activity that could not be attributed to IL-1, IL-3, IL-4, IL-5, IL-6, GM-CSF, G-CSF, macrophage CSF (M-CSF), or stem cell factor. The transfer of activated NK cells with BMC into lethally irradiated syngeneic mice resulted in greater BMC engraftment in the recipients. Thus, these results using a pure population of activated NK cells indicate that when activated, these cells can produce a variety of growth factors for hematopoiesis and exert significant hematopoietic growth-promoting effects in vivo.     

Granulocyte-macrophage colony-stimulating factor augments phagocytosis of Mycobacterium avium complex by human immunodeficiency virus type 1-infected monocytes/macrophages in vitro and in vivo

The role of human immunodeficiency virus type 1 (HIV-1) infection on the ability of human monocytes/macrophages to phagocytose Mycobacterium avium complex (MAC) in vivo and in vitro and the effect of granulocyte-macrophage colony-stimulating factor (GM-CSF) on this function were investigated. By use of a flow cytometric assay to quantify phagocytosis, HIV-1 infection was found to impair the ability of monocyte-derived macrophages to phagocytose MAC in vitro, whereas GM-CSF significantly improved this defect. Phagocytosis was not altered by exposure to a mutant form of GM-CSF (E21R) binding only to the alpha chain of the GM-CSF receptor, suggesting that signaling by GM-CSF that leads to augmentation of phagocytosis is via the beta chain of the receptor. In a patient with AIDS and disseminated multidrug-resistant MAC infection, GM-CSF treatment improved phagocytosis of MAC by peripheral blood monocytes and reduced bacteremia. These results imply that GM-CSF therapy may be useful in restoring antimycobacterial function by human monocytes/macrophages.     

Effect of granulocyte-macrophage colony-stimulating factor treatment on phenotype,cytokine release and cytotoxicity of circulating blood monocytes and monocyte-derived macrophages

We studied phenotype, function and differentiation of mononuclear phagocytes in 11 cancer patients treated subcutaneously with 10 μg/kg recombinant human (rhu) GM-CSF for 7 d. The rhuGM-CSF treatment induced (1) a 5.9-fold increase in the number of blood monocytes (MO), (2) a decrease of CD14^bright/CD16^bright cells with a diminution of the mean fluorescence intensity (MFI) of CD14, and (3) a decrease of MO cellular cytotoxicity. In patients' sera, tumour necrosis factor (TNF)-α, interleukin (IL)-10, IL-12, neopterin, macrophage-colony-stimulating factor (M-CSF), and IL-1 receptor antagonist (IL-1RA) increased, whereas GM-CSF and granulocyte-colony-stimulating factor (G-CSF) decreased after an initial peak. In whole blood samples the lipopolysaccharide (LPS)-stimulated release of TNF-α, IL-6 and IL-1RA increased initially, whereas IL-1β, IL-10 and IL-12 decreased. During differentiation from MO to macrophages (MAC), interferon (IFN)-γ-stimulated tumour cytotoxicity increased, but both MO and MAC were less cytotoxic upon rhuGM-CSF treatment. The differentiation-associated increase of LPS-induced TNF-α, IL-1RA and IL-10 secretion was reduced by the rhuGM-CSF treatment, and the expression of CD14 on MAC as well as the proportion of CD14⁺/CD16⁺, CD14⁺/MAX.1⁺ and CD14⁺/CD71⁺ cells in 7-d cultured MAC declined. We interpret these findings as (1) an increase of immature MO upon rhuGM-CSF therapy, (2) a priming effect on the LPS-induced proinflammatory cytokine repertoire of MO, and (3) an impact of rhuGM-CSF on the capacity of MO to differentiate to MAC in vitro.     

HIV-1 exposed dendritic cells show increased pro-inflammatory cytokine production but reduced IL-1ra following lipopolysaccharide stimulation.

OBJECTIVES: Dendritic cells (DC) are potential first target cells in sexually transmitted HIV-1 infection. They are also considered to be central in the activation of naive T cells, which thereupon can become permissive for HIV-1. In addition, activated DC express effector molecules, which likely contribute to the direction of T helper (Th1/Th2)-specific immune responses. METHODS: The capacity of cytokine and chemokine production in in vitro DC infected and uninfected with HIV-1 was assessed by enzyme-linked immunosorbent assay (ELISA) and by in situ immunocytochemical detection at the single cell level. Fluorescent in situ 5'-nuclease assay (FISNA) was used for quantitative evaluation of HIV-1 gag-positive cells. RESULTS: Macrophage-tropic HIV-1 effectively infected 20-40% of in vitro cultured DC. However, this activity alone did not induce detectable cytokine or chemokine protein expression in DC. In contrast, lipopolysaccharide (LPS) stimulation of these HIV-1-infected DC resulted in a significantly increased level of cells producing tumour necrosis factor alpha (TNF-alpha) and interleukin (IL) 1beta but reduced frequencies of cells producing IL-1 receptor antagonist (IL-1ra) compared with the LPS-stimulated but uninfected DC cultures (P < 0.05). Furthermore, an extensive production of the beta-chemokines [RANTES, macrophage inflammatory proteins (MIP) 1alpha and 1beta] was detected in DC in response to both LPS and HIV-1 plus LPS. CONCLUSIONS: These findings indicate that HIV-1 infected DC may have an increased proinflammatory activity. Elevated production of cytokines such as TNF-alpha and IL-1beta and reduced IL-1ra may contribute to enhanced replication of HIV-1 in bystander T cells. Gram-negative bacterial infection and gut-associated bacterial translocation in HIV-1-infected individuals may also result in endotoxin-mediated reactivation of HIV-1 in bystander CD4 CD45RO T cells caused by the increased production of proinflammatory cytokines in DC.     

Proinflammatory cytokines and chemokine production and expression by human osteoblasts isolated from patients with rheumatoid arthritis and osteoarthritis

OBJECTIVE: To evaluate whether subchondral osteoblasts (OB) are involved in the production of cytokines and chemokines in rheumatic diseases. METHODS: OB were isolated from subchondral bone of rheumatoid arthritis (RA), osteoarthritis (OA) and post-traumatic (PT) patients, cultured in vitro in the presence or absence of interleukin 1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha), and assessed for the production, immunolocalization, and mRNA expression of proinflammatory cytokines (IL-1alpha, IL-1beta, TNF-alpha) and alpha and beta chemokines [IL-8, growth related gene product (GRO-alpha), monocyte chemoattractant protein 1 (MCP-1), RANTES, and macrophage inflammatory proteins MIP-1alpha, MIP-1beta]. RESULTS: Cultured OB from different patients did not release IL-1alpha, IL-1beta, or TNF-alpha, and constitutively secreted IL-8, GRO-alpha, and MCP-1, while RANTES, MIP-1alpha, MIP-1beta were undetectable or near the lower level of sensitivity of the immunoenzymatic assay. GRO-alpha was significantly higher in RA than in OA and PT patients. IL-1beta and TNF-alpha alone or in combination strongly stimulated chemokine release by OB. Only RANTES production was not increased by the combination of the 2 cytokines. IL-1alpha, IL-1beta, and TNF-alpha were expressed as cytoplasmic proteins and were not secreted by OB even after stimulation. CONCLUSION: OB from subchondral bone release chemokines that could be involved in the mechanisms that directly or indirectly cause bone remodelling and cartilage destruction.     

Early immune activation in gut-associated and peripheral lymphoid tissue during acute HIV infection

OBJECTIVE: To study innate and adaptive immune responses in gut-associated lymphoid tissue (GALT) as well as peripheral lymphoid tissue (pLT) obtained from individuals with acute HIV-1 infection syndrome. DESIGN: The expression of chemokines [regulated upon activation: normal T cell expressed/secreted (RANTES), macrophage-inflammatory protein (MIP) 1alpha/beta], cytokines (IL-1beta, TNF-alpha, IL-12, IL-4, IL-10, IL-2, IFN-gamma) and cytotoxic effector molecules (granzyme A, perforin) and cell marker (CD8) were analysed at the single cell level in GALT and pLT of patients experiencing acute HIV-1 infection (day -3 to 48 days from onset of acute symptoms). RESULTS: Substantial pro-inflammatory immune responses (TNF-alpha, IL-1beta, IL-12) and expansion in the CD8 T-cell population were noted in both compartments compared with uninfected controls. This was associated with an early increased expression of beta-chemokines (RANTES, MIP-1alpha/beta) and granzyme, but not with an increase in the expression of perforin. The upregulation of IL-2, IL-12 and IL-4 was noted in both pLT and GALT, whereas IL-10 expression was mainly increased in GALT. CONCLUSION: Taken together, these findings demonstrate that there was a broad and early immune activation in GALT and pLT during acute HIV-1 infection. The relative lack of perforin expression in both GALT and pLT, however, questions the functional efficacy of the observed immune activation in generating cytotoxic T cells that were able to eliminate HIV-infected cells.     

Chemokine production by human chondrocytes.

OBJECTIVE: To evaluate the role of chondrocytes in producing CXC chemokines [interleukin 8 (IL-8), growth related gene product (GRO-alpha)] and CC chemokines [monocyte chemoattractant protein (MCP-1), macrophage inflammatory protein (MIP-1alpha), RANTES] in patients with rheumatoid arthritis (RA) and osteoarthritis (OA) and subjects after traumatic injury (PT). METHODS: Articular cartilage specimens were obtained from 38 patients with OA and 18 with RA undergoing joint replacement surgery. Healthy human cartilage was obtained from femoral condyles removed after trauma in 11 subjects with no history of joint pathology (PT cases). Chondrocytes were isolated from articular cartilage by sequential enzymatic digestion and cultured in vitro. Chemokine production was investigated in unstimulated condition and after 72 h incubation with proinflammatory [IL-1beta, tumor necrosis factor-alpha (TNF-alpha)] and antiinflammatory [transforming growth factor-beta1 (TGF-beta1), IL-10] mediators. Chemokine concentrations in cell supernatants were evaluated by ELISA. RESULTS: Chondrocytes produce all these chemokines to a different extent. IL-1beta was a more potent stimulus than TNF-alpha in inducing production of all chemokines except MCP-1. We found no statistical differences among chondrocytes isolated from OA, RA, and PT for chemokine production in either basal conditions or after cytokine stimulation. IL-1beta induced chemokine production can be modulated by TGF-beta1 in different ways according to the various chemokines, while IL-10 does not affect IL-1beta induced chemokine production. CONCLUSION: Chondrocytes produce IL-8, GRO-alpha, MCP-1, MIP-1alpha, and RANTES. Proinflammatory factors (IL-1beta, TNF-alpha) effectively upregulate chemokine production, but production is scarcely modulated by the antiinflammatory mediators TGF-beta and IL-10. Chondrocyte derived chemokines may play a role in triggering the mechanisms involved in pathogenesis and persistence of joint diseases.     

Cytokine production by primary bone marrow megakaryocytes

Primary human bone marrow megakaryocytes were studied for their ability to express and release cytokines potentially relevant to their proliferation and/or differentiation. The purity of the bone marrow megakaryocytes was assessed by morphologic and immunocytochemical criteria. Unstimulated marrow megakaryocytes constitutively expressed genes for interleukin-1 beta (IL-1 beta), IL-6, granulocyte-macrophage colony-stimulating factor (GM-CSF), and tumor necrosis factor-alpha (TNF-alpha), by the polymerase chain reaction (PCR) and Northern blot analysis. At the protein level, megakaryocytes secreted significant amounts of IL-1 beta (53.6 +/- 3.6 pg/mL), IL-6 (57.6 +/- 15.6 pg/mL), and GM-CSF (24 +/- 4 pg/mL) but not TNF-alpha. Exposure of human marrow megakaryocytes to IL-1 beta increased the levels of IL-6 (87.3 +/- 2.3 pg/mL) detected in the culture supernatants. Transforming growth factor- beta was also able to stimulate IL-6, IL-1 beta, and GM-CSF secretion, but was less potent than stimulation with phorbol-12-myristate-13- acetate (PMA). The secreted cytokines acted additively to maintain and increase the number of colony-forming unit-megakaryocytes colonies (approximately 35%). These studies demonstrate the production of multiple cytokines by isolated human bone marrow megakaryocytes constitutively or stimulated in vitro. The capacity of human megakaryocytes to synthesize several cytokines known to modulate hematopoietic cells supports the concept that there may be an autocrine mechanism operative in the regulation of megakaryocytopoiesis.     

Macrophage-active colony-stimulating factors enhance human immunodeficiency virus type 1 infection in bone marrow stem cells.

To define the relationship between human immunodeficiency virus type 1 (HIV-1) infection in hematopoietic stem cells and virus production by their progeny, we performed kinetic studies infecting bone marrow (BM) stem cells and culturing them in the presence of hematopoietic growth factors. CD34-positive (CD34+), CD4-negative (CD4-) BM cells were isolated and infected in vitro with the monocytotropic HIV-1JR-FL strain or the laboratory-maintained HTLV-IIIB strain at a high multiplicity of infection. The cells were susceptible to productive infection only with HIV-1JR-FL, and virus production as measured by p24 protein release was markedly increased (more than fivefold) in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-3 (IL-3). Macrophage CSF (M-CSF) was less stimulatory and granulocyte CSF (G-CSF) had no effect on virus production. Virus production coincided with proliferation of mononuclear phagocytes but was not related to granulocytic proliferation in G-CSF-treated BM cultures. Although peak virus production from GM-CSF-treated macrophages occurred 2 to 3 weeks after infection, peak virus production in infected stem cells was observed 5 to 6 weeks after. Enhancement in virus production had a more rapid onset when CD34+/CD4- cells were cultured in the presence of both GM-CSF and IL-3 for 7 or 14 days. Under these conditions there was a 10-fold enhancement in virus production after 7 days of preincubation and a 50-fold enhancement after 14 days. These data indicate that while the stem cell compartment may be susceptible to infection with a monocytotropic HIV-1 strain, productive and sustained infection is realized only after macrophage differentiation. The lack of effect of G-CSF on virus production is likely because of the limited effect of this hematopoietin on mononuclear phagocyte generation and function.