Bone Marrow Stroma-Derived Prolactin Is Involved in Basal and Platelet-Activating Factor–Stimulated In Vitro Erythropoiesis

Single Nucleotide Polymorphisms of Immunity-Related Genes and Their Effects on Immunophenotypes in Different Pig Breeds

Enhancing resistance and tolerance to pathogens remains an important selection objective in the production of livestock animals. Single nucleotide polymorphisms (SNPs) vary gene expression at the transcriptional level, influencing an individual's immune regulation and susceptibility to diseases. In this study, we investigated the distribution of SNP sites in immune-related genes and their correlations with cell surface markers of immune cells within purebred (Taiwan black, Duroc, Landrace and Yorkshire) and crossbred (Landrace-Yorkshire) pigs. Thirty-nine SNPs of immune-related genes, including 11 cytokines, 5 chemokines and 23 Toll-like receptors (TLRs) (interferon-α and γ (IFN-α, γ), tumor necrosis factor-α (TNF-α), granulocyte-macrophage colony-stimulating factor (GM-CSF), Monocyte chemoattractant protein-1 (MCP-1) and TLR3, TLR4, TLR7, TLR8, and TLR9) were selected, and the percentages of positive cells with five cell surface markers of CD4, CD8, CD80/86, MHCI, and MHCII were analyzed. There were 28 SNPs that were significantly different among breeds, particularly between Landrace and Taiwan black. For instance, the frequency of SNP1 IFN-α -235A/G in Taiwan black and Landrace was 11.11% and 96.15%, respectively. In addition, 18 SNPs significantly correlated with the expression of cell surface markers, including CD4, CD8, CD80/86, and MHCII. The percentage of CD4+ (39.27%) in SNP33 TLR-8 543C/C was significantly higher than those in A/C (24.34%), at p < 0.05. Together, our findings show that Taiwan black pigs had a unique genotype distribution, whereas Landrace and Yorkshire had a more similar genotype distribution. Thus, an understanding of the genetic uniqueness of each breed could help to identify functionally important SNPs in immunoregulation.

Acute myeloid leukemia presenting as galactorrhea

Acute myeloid leukemia (AML) presents with symptoms related to pancytopenia (weakness, infections, bleeding diathesis) and organ infiltration with leukemic cells. Galactorrhea is an uncommon manifestation of AML. We report a case of AML presenting with galactorrhea.

Autocrine/paracrine roles of extrapituitary growth hormone and prolactin in health and disease: An overview

Growth hormone (GH) and prolactin (PRL) are both endocrines that are synthesized and released from the pituitary gland into systemic circulation. Both are therefore hormones and both have numerous physiological roles mediated through a myriad of target sites and both have pathophysiological consequences when present in excess or deficiency. GH or PRL gene expression is not, however, confined to the anterior pituitary gland and it occurs widely in many of their central and peripheral sites of action. This may reflect "leaky gene" phenomena and the fact that all cells have the potential to express every gene that is present in their genome. However, the presence of GH or PRL receptors in these extrapituitary sites of GH and PRL production suggests that they are autocrine or paracrine sites of GH and PRL action. These local actions often occur prior to the ontogeny of pituitary somatotrophs and lactotrophs and they may complement or differ from the roles of their pituitary counterparts. Many of these local actions are also of physiological significance, since they are impaired by a blockade of local GH or PRL production or by an antagonism of local GH or PRL action. These local actions may also be of pathophysiological significance, since autocrine or paracrine actions of GH and PRL are thought to be causally involved in a number of disease states, particularly in cancer. Autocrine GH for instance, is thought to be more oncogenic than pituitary GH and selective targeting of the autocrine moiety may provide a therapeutic approach to prevent tumor progression. In summary, GH and PRL are not just endocrine hormones, as they have autocrine and/or paracrine roles in health and disease.

Ames hypopituitary dwarf mice demonstrate imbalanced myelopoiesis between bone marrow and spleen

Ames hypopituitary dwarf mice are deficient in growth hormone, thyroid-stimulating hormone, and prolactin. The phenotype of these mice demonstrates irregularities in the immune system with skewing of the normal cytokine milieu towards a more anti-inflammatory environment. However, the hematopoietic stem and progenitor cell composition of the bone marrow (BM) and spleen in Ames dwarf mice has not been well characterized. We found that there was a significant decrease in overall cell count when comparing the BM and spleen of 4-5 month old dwarf mice to their littermate controls. Upon adjusting counts to differences in body weight between the dwarf and control mice, the number of granulocyte-macrophage progenitors, confirmed by immunophenotyping and colony-formation assay was increased in the BM. In contrast, the numbers of all myeloid progenitor populations in the spleen were greatly reduced, as confirmed by colony-formation assays. This suggests that there is a shift of myelopoiesis from the spleen to the BM of Ames dwarf mice; however, this shift does not appear to involve erythropoiesis. The reasons for this unusual shift in spleen to marrow hematopoiesis in Ames dwarf mice are yet to be determined but may relate to the decreased hormone levels in these mice.

The prolactin gene: a paradigm of tissue-specific gene regulation with complex temporal transcription dynamics

Transcription of numerous mammalian genes is highly pulsatile, with bursts of expression occurring with variable duration and frequency. The presence of this stochastic or 'noisy' expression pattern has been relatively unexplored in tissue systems. The prolactin gene provides a model of tissue-specific gene regulation resulting in pulsatile transcription dynamics in both cell lines and endocrine tissues. In most cell culture models, prolactin transcription appears to be highly variable between cells, with differences in transcription pulse duration and frequency. This apparently stochastic transcription is constrained by a transcriptional refractory period, which may be related to cycles of chromatin remodelling. We propose that prolactin transcription dynamics result from the summation of oscillatory cellular inputs and by regulation through chromatin remodelling cycles. Observations of transcription dynamics in cells within pituitary tissue show reduced transcriptional heterogeneity and can be grouped into a small number of distinct patterns. Thus, it appears that the tissue environment is able to reduce transcriptional noise to enable coordinated tissue responses to environmental change. We review the current knowledge on the complex tissue-specific regulation of the prolactin gene in pituitary and extra-pituitary sites, highlighting differences between humans and rodent experimental animal models. Within this context, we describe the transcription dynamics of prolactin gene expression and how this may relate to specific processes occurring within the cell.

PAF-acetylhydrolase expressed during megakaryocyte differentiation inactivates PAF-like lipids

Platelet activating factor (PAF) and PAF-like lipids induce inflammatory responses in target cells. These lipid mediators are inactivated by PAF-acetylhydrolase (PAF-AH). The PAF signaling system affects the growth of hematopoietic CD34(+) cells, but roles for PAF-AH in this process are unknown. Here, we investigated PAF-AH function during megakaryopoiesis and found that human CD34(+) cells accumulate this enzymatic activity as they differentiate toward megakaryocytes, consistent with the expression of mRNA and protein for the plasma PAF-AH isoform. Inhibition of endogenous PAF-AH activity in differentiated megakaryocytes increased formation of lipid mediators that signaled the PAF receptor (PAFR) in fully differentiated human cells such as neutrophils, as well as megakaryocytes themselves. PAF-AH also controlled megakaryocyte alpha(IIb)beta(3)-dependent adhesion, cell spreading, and mobility that relied on signaling through the PAFR. Together these data suggest that megakaryocytes generate PAF-AH to modulate the accumulation of intracellular phospholipid mediators that may detrimentally affect megakaryocyte development and function.

Pregnancy and lactation modulate maternal splenic growth and development of the erythroid lineage in the rat and mouse

Maternal physiology changes dramatically during the course of gestation and lactation to meet the needs of the developing fetus and newborn. In the present study, we examined the influence of pregnancy and lactation on growth and erythroid gene expression patterns of the maternal spleen. Holtzman Sprague-Dawley rats and CD-1 mice were killed at various stages of gestation and post partum. We observed pregnancy dependent increases in spleen weight and spleen DNA content in both the rat and mouse. In the rat, spleen size was greatest at the end of pregnancy and regressed post partum. In contrast, mouse spleen size peaked by gestational Day 13 and regressed to its non-pregnant weight before parturition. Pregnancy dependent changes in the size of the spleen were primarily due to an increase in red pulp. Maternal spleen expression of erythroid-associated genes (erythroid Krüppel-like factor, erythroid 5-aminolevulinate synthase-2, β-major globin) was influenced by pregnancy and lactation. A pregnancy dependent increase in erythroid progenitors was also observed. In summary, the demands of pregnancy and lactation cause marked adaptations in the maternal spleen. The maternal spleen increases in size and exhibits an expansion of the erythroid lineage.

Acute myeloid leukaemia presenting as galactorrhoea

The clinical presentation of acute myeloid leukaemia is variable. We report a 40-year-old woman who presented with a 1-month history of galactorrhoea with an elevated prolactin level. The blood counts were normal, but she was found to have acute myeloid leukaemia with monocytic differentiation. The serum prolactin level normalized after chemotherapy. In the absence of evidence of CNS involvement, the hyperprolactinaemia is presumed to be a paraneoplastic phenomenon. We discuss the potential mechanism of prolactin production in this case.

Prolactin expression is induced in Jurkat T-cells by beta-catenin LEF-1, AP-1 and cAMP

Prolactin (PRL) in humans is produced in the pituitary as well as in extra-pituitary sites. A proximal promoter that requires the Pit-1 transcription factor controls pituitary PRL expression, whereas a distal (upstream) promoter located at 5.8 kb upstream of the pituitary start site regulates extra-pituitary PRL synthesis. We have previously reported that cAMP regulates PRL transcription in Jurkat lymphocytes in part through a cAMP responsive element. Here we demonstrate that additional PRL regulatory elements corresponding to LEF-l and AP-1 transcription factor binding sites appear important for PRL expression, since factor binding by EMSA and reporter gene expression are reduced when these sites are deleted or mutated. Interestingly, over-expression of a constitutively active form of beta-catenin increases PRL expression of Jurkat cells. This effect occurs through both LEF-dependent and -independent pathways. Our studies identify the distal PRL promoter as a target for beta-catenin, and reveal novel pathways regulating extra-pituitary PRL expression.

Stress and prolactin effects on bone marrow myeloid cells, serum chemokine and serum glucocorticoid levels in mice

OBJECTIVE

Current evidence supports the conclusion that prolactin (PRL) is not an obligate immunoregulatory hormone and influences the immune system predominantly during stress conditions. In this study, we examined the impact of PRL on the psychogenic stress-induced responses of myeloid cells.

METHODS

Seven-week-old PRL+/- (normal) and PRL-/- (deficient) mice were exposed to a predator for 1 h/day on 3 consecutive days. Another group of PRL-deficient mice received either 1 pituitary graft (hyperprolactinemic) or sham surgery at 5 weeks of age, while PRL-normal mice only received sham surgery. Two weeks later, these mice were also subjected to predator exposure. One day after the last predator exposure session, all mice were killed and the bone marrow and blood harvested.

RESULTS

Significant differences in the myeloid cells between PRL-normal and PRL-deficient mice only occurred in stressed conditions. The median serum corticosterone levels were consistently higher in PRL-deficient mice. The implantation of a pituitary graft lowered the corticosterone levels to those observed in PRL-normal mice. The absolute number of immature neutrophils as well as the numbers of granulocyte macrophage, monocyte/macrophage and granulocyte colonies were significantly higher in the stressed PRL-deficient mice; however, only the increased number of immature neutrophils was reversed by pituitary grafting.

CONCLUSIONS

Our findings support previous observations that PRL influences myeloid cells of the bone marrow most profoundly in stressed conditions. However, the mechanism by which PRL influences bone marrow myeloid cells during stress cannot be explained solely by its effect on serum corticosterone.

Therapeutic potential of S179D prolactin – from prostate cancer to angioproliferative disorders: the first selective prolactin receptor modulator

Increasing evidence suggests an important role for autocrine/paracrine prolactin in breast and prostate cancers and other disease states. Prolactin production in these extrapituitary sites is not governed by dopamine agonists, a finding that has spurred the production of prolactin receptor antagonists. This review focuses on one such antagonist, S179D prolactin, which was produced by mimicking a natural antagonist, phosphorylated prolactin. S179D prolactin is a very effective growth antagonist, partly because it inhibits signalling from unmodified prolactin and partly because it produces its own intracellular signal. This signal results in cell differentiation, cell-cycle arrest or apoptosis depending on dose, duration of treatment and cellular context. S179D prolactin is also a potent antiangiogenic and initial studies have shown it to be a potent anti-inflammatory agent. In light of these additional modes of action, it is suggested that S179D prolactin should now be more aptly referred to as a selective prolactin receptor modulator.

Successful treatment of Diamond-Blackfan anemia with metoclopramide

Diamond-Blackfan anemia (DBA) is a congenital anemia characterized by a low reticulocyte count, the absence or severe reduction of hemoglobin-containing cells in the bone marrow, and normal megakaryocytic and granulocytic differentiation. Although the anemia may initially respond to corticosteroid therapy, many patients require lifelong red blood cell (RBC) transfusion, leading to infectious complications and iron overload. Metoclopramide has recently been used to treat DBA. Treatment with metoclopramide induces the release of prolactin from the pituitary and stimulates erythropoiesis. For these reasons, we used metoclopramide to treat a 20-year-old man with DBA refractory to low and high doses of corticosteroids, cyclosporin A, and tacrolimus (FK506). The hemoglobin and hematocrit slowly increased, and he has remained asymptomatic and transfusion-independent for 8 months. Metoclopramide therapy should be considered in patients with refractory DBA before treatment-related complications develop.

Immunologic and hematopoietic effects of recombinant human prolactin after syngeneic bone marrow transplantation in mice

The period of immune deficiency following bone marrow transplantation (BMT) results in a susceptibility to opportunistic infections and remains a growing obstacle in improving the efficacy of BMT. Neuroendocrine hormones have been shown to affect numerous immunologic and hematologic responses after in vivo administration. We investigated whether neuroendocrine hormones, notably prolactin (PRL), could be administered after BMT and result in improved immunologic recovery. Mice were given lethal total body irradiation followed with a congeneic or a syngeneic BMT. Some groups then received recombinant human PRL (rhPRL) daily for 3 weeks. Effects on immune reconstitution and function were then monitored. The results show that PRL could increase thymic cellularity and donor T-cell reconstitution after congeneic BMT. Increases in B cells and myeloid progenitors were also observed. Mitogenic responses by both T and B cells were observed after PRL treatment. These results suggest that PRL may be of use to promote immune and myeloid reconstitution after BMT.

Platelet-activating factor and normal or leukaemic haematopoiesis

Platelet-activating factor (PAF), a phospholipid mediator with a wide range of actions on mature leukocytes, acts directly during early human haematopoiesis by affecting the growth of haematopoietic progenitors and indirectly, by modulating cytokine synthesis by bone marrow stromal cells. At this time, its role during leukaemic diseases remains speculative. The lack of membrane PAF receptor (PAF-R) on leukaemic blasts suggest that this receptor represents a marker of mature cells and its membrane induction a consequence of cell maturation. While the couple PAF/PAF-R has been largely studied using B cell lines, few results are available using B cells of patients with haematopoietic malignancies casting some doubts concerning the potential role (if any) of this molecule during leukaemic diseases.

Response of Diamond-Blackfan anemia to metoclopramide: evidence for a role for prolactin in erythropoiesis

A 47-year-old woman with severe macrocytic anemia markedly improved during the second and third trimesters of 3 pregnancies and when breast-feeding her 2 children. Because the serum prolactin level is elevated at these times, we later treated her with metoclopramide (10 mg orally 3 times daily), a medication known to induce prolactin release. Her serum prolactin levels increased from 7 to 133 ng/mL (normal < 20 ng/mL) and hematocrit from 17% to 22% to 35%. With continued therapy (now 10 mg orally daily), her hematocrit has ranged from 30% to 40% for 6 years, although the macrocytosis persists (mean corpuscular volume, 100-112 fL). On the basis of this observation, a pilot study was undertaken of metoclopramide therapy in patients with Diamond-Blackfan anemia who were refractory to low doses of corticosteroids. Fifteen patients were enrolled and 9 completed the planned 16 weeks of therapy. Three individuals responded, suggesting that this therapeutic approach may benefit others. As with the index case, the anemia did not improve until 12 to 15 weeks of therapy had been completed.

Effect of prolactin on the antigen presenting function of monocyte-derived dendritic cells

Monocyte derived macrophages (Mphi) and dendritic cells (DC) play critical roles at the interface between innate and adaptive immunity. Both types of cells can effectively phagocytose exogenous antigens, whereas only DC can process and present them efficiently to antigen-specific T lymphocytes. The hormone PRL is also produced by immune cells and is regarded as a key component of the neuroendocrine--immune loop and a local regulator of lymphocyte response. Its main feature is cooperation with cytokines and hemopoietins. Triggering of monocyte PRL receptors with physiological-to-supraphysiological concentrations of PRL up-regulates the GM-CSF receptors, resulting in synergistic PRL-GM-CSF induced maturation of immature (i)DC. Further incubation induces increased antigen-presenting activity at the highest PRL concentrations studied (200 ng/ml). IFN-gamma, release by allogeneic lymphocytes is dependent on T cell-triggered IL-12 release by PRL-preincubated iDC. This, in turn, may be secondary to increased DC expression of CD40 or IFN-gamma. The permissive action of high PRL concentrations in the antigen presenting process may be of significance in initiation of the response against major histocompatibility complex (MHC)-presented self-antigens and may explain the association of hyperprolactinemia with autoimmune diseases.

Effects of prolactin on hematopoiesis

The presence of extra-pituitary prolactin and its cognitive receptors in the hematopoietic micro-environment raises the question of whether prolactin plays a role in lympho-hematopoiesis and under what conditions. Current studies suggest that endogenous prolactin does not play a significant role under normal steady-state conditions. Rather, prolactin has been implicated as a 'stress hormone', functioning to restore hematopoietic homeostasis under conditions of dysregulation. The stress response of prolactin as well as its complex relationship with other hormones and factors has resulted in conflicting reports in the literature regarding prolactin's role in lympho-hematopoiesis. A review of this literature is provided as well as discussion of conditions under which lymphohematopoietic activity of prolactin may be evident.

Prolactin production by immune cells

Prolactin (PRL) is a pituitary hormone and a cytokine that plays an important role in rodent and human immune responses, including autoimmune diseases. However, many cells and tissues other than the pituitary make PRL, including immune cells. Here, we will present the evidence demonstrating PRL synthesis by different subtypes of immune cells from humans, mice and rats, describe the regulation of PRL gene expression in human lymphocytes, and discuss the functions of PRL made by immune cells. Finally, we will present evidence for involvement of immune cell PRL in human autoimmune disease and suggest how it might play a unique immunoregulatory role.

Prolactin-induced expression of cytokine-inducible SH2 signaling inhibitors in human hematopoietic progenitors

OBJECTIVE

The prolactin (PRL) receptor (PRLR) utilizes the JAK2/STAT-5 pathway and induces expression of cytokine-inducible SH2 (CIS)/JAK2 binding (JAB) signaling inhibitors. We and others recently showed that CIS-3 and JAB abolish PRLR-mediated JAK2 activation and STAT-5 activity, whereas CIS-1, CIS-2, and CIS-4 had a negligible effect. Human CD34(+) hematopoietic progenitors express PRLRs and respond to PRL in vitro by enhanced cytokine-induced colony formation. To assess the signaling mechanism(s) involved in PRL-mediated enhancement of hematopoiesis and to identify further the CIS/JAB targets for PRL-mediated cellular responses, we assayed the effect of PRL, alone or in the presence of interleukin-3 (IL-3), on activation of STAT-5 and expression of CIS/JAB RNA in human cord blood (CB) CD34(+) cells.

MATERIALS AND METHODS

Isolated CB CD34(+) cells were incubated in serum-free cultures in the absence or presence of recombinant human (rh)PRL, rhIL-3, or both. Cell lysates were subjected to Western blot analysis with anti-STAT-5 and anti-phospho-STAT-5 antibodies. Isolated RNA was subjected to semiquantitative reverse transcriptase polymerase chain reaction analysis of CIS/JAB expression.

RESULTS

STAT-5 tyrosine phosphorylation was similarly induced by PRL and IL-3, with an additive effect detected in the presence of both stimuli. Both PRL and IL-3, alone or combined, failed to induce CIS-3 or JAB RNA expression in CD34(+) cells. Interferon-gamma had no effect on CIS-3/JAB induction in these cells. However, CIS-1 was induced by PRL < IL-3 < PRL+IL-3, whereas CIS-2 expression was induced by PRL = IL-3 < PRL+IL-3.

CONCLUSIONS

Our findings show that PRL induces activation of STAT-5 and expression of similar CIS/JAB family members as IL-3 does in human CB CD34(+) cells. Because CIS-1 abolishes STAT-5 activation via the IL-3 but not the PRL receptor, the hematopoietic growth-promoting effects of PRL may involve its capacity to provide sustained STAT-5-mediated stimulatory signals to the cells.

Growth hormone and prolactin expression in the immune system

Prolactin (PRL) and growth hormone (GH) are pituitary hormones that play pivotal roles in lactation and body growth, respectively. In addition, both hormones have been implicated as modulators of immune responses. Since the expression of GH and PRL by leukocytes points to autocrine or paracrine roles during immune responses, our study is aimed at PRL- and GH-production in leukocytes. We show that human peripheral blood granulocytes, which express GH and PRL mRNA, contain high molecular-weight immunoreactive variants of GH and PRL (37 and 43 kDa, respectively), but not the pituitary-sized hormones. Secretion of these variants, or biologically active material as assessed by the Nb2 bioassay, was not detected. On the other hand, certain leukemic myeloid cells secrete 23-kDa, pituitary-sized, PRL, which is biologically active.

Major hematologic diseases in the developing world- new aspects of diagnosis and management of thalassemia, malarial anemia, and acute leukemia

The three presentations in this session encompass clinical, pathophysiological and therapeutic aspects of hematologic diseases which impact most heavily on developing world countries. Dr. Victor Gordeuk discusses new insights regarding the multi-faceted pathogenesis of anemia in the complicated malaria occurring in Africa. He describes recent investigations indicating the possible contribution of immune dysregulation to this serious complication and the implications of these findings for disease management. Dr. Surapol Issaragrisil and colleagues describe epidemiologic and clinical characteristics of the thalassemic syndromes. In addition to being considered a major health problem in Southeast Asia, the migration throughout the world of people from this region has caused the disease to have global impact. A unique thalassemia variant, Hb Ebeta-thalassemia, with distinctive clinical features, has particular relevance for this demographic issue. Special focus will be reported regarding recent prenatal molecular screening methods in Thailand which have proven useful for early disease detection and disease control strategies. Dr. Raul Ribeiro describes a clinical model for providing effective treatment for a complex malignancy (childhood acute lymphoblastic leukemia) in countries with limited resources. With the multidisciplinary approach in Central American of the joint venture between St. Jude Children's Research Hospital International Outreach Program and indigenous health care personnel, major therapeutic advances for this disease have been achieved. Given the major demographic population shifts occurring worldwide, these illnesses also have important clinical implications globally. These contributions demonstrate that lessons learned within countries of disease prevalence aid our understanding and management of a number of disorders prominently seen in developed countries. They will show how effective partnerships between hematologists in more and less developed nations may work together to produce important advances for treating major hematologic diseases in less developed regions. A major focus relates to the socio-economic and medical burden of these diseases in developing countries with limited resources. As such, these problems provide a challenge and an opportunity for collaborative interaction between hematologists and policy makers worldwide.

Individual and combined effect of granulocyte-macrophage colony-stimulating factor and prolactin on maturation of dendritic cells from blood monocytes under serum-free conditions

Prolactin (PRL) shares structural and functional features with haemopoietic factors and cytokine peptides. Dendritic cells (DC) are involved in both initiating the primary and boosting the secondary host immune response and can be differentiated in vitro from precursors under the effect of granulocyte-macrophage colony-stimulating factor (GM-CSF) plus other factors. Because PRL has been shown to functionally interact with GM-CSF, we have addressed its role on GM-CSF-driven differentiation of DC. Monocytic DC precursors from peripheral blood mononuclear cells (PBMC) were enriched either by adhesion to a plastic surface or CD14-positive selection and cultured for 7 days in serum-free medium containing GM-CSF, interleukin (IL)-4 and PRL, alone or in combination. Cells with large, veiled cytoplasm, expressing major histocompatibility complex (MHC) class II and the costimulatory molecules CD80, CD86 and CD40 and lacking the monocyte marker CD14, were considered as having the phenotype of cytokine-generated DC. Functional maturation was assessed by proliferation and interferon-gamma (IFN-gamma) release of allogeneic T lymphocytes. Physiological (10-20 ng/ml) concentrations of PRL interacted synergistically with GM-CSF and the effect was similar to that induced by IL-4 on GM-CSF-driven DC maturation. When used alone, the physiological concentrations of PRL were inhibitory, whereas higher concentrations (80 ng/ml) were stimulatory. The synergistic effect of PRL may in part be caused by its ability to counteract the down-modulation of the GM-CSF receptor observed in serum-free conditions. These data provide further evidence of the significance of PRL in the process of T lymphocyte activation.

Association between elevated prolactin levels and circulating erythroid precursors in dialyzed patients

The prolactin (PRL) receptor (R), a member of the cytokine hemopoietin receptor superfamily, has been shown to activate early differentiation steps along the erythroid pathway. In particular PRL, a product of bone marrow stroma, induces functional erythropoietin (EPO)-R on CD34+ hemopoietic progenitors. In this study, expression of EPO-R mRNA and responsiveness to EPO were assessed on enriched hemopoietic progenitor cells (HPC) from seven hyperprolactinemic and three normoprolactinemic patients and two normal subjects. Expression of EPO-R mRNA by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) was found in HPC of four out of seven hyperprolactinemic patients but not in normoprolactinemic patients or normal donors. Development of EPO-dependent Colony Forming Unit-Erythroid (CFU-E) colonies in semi-solid medium was observed only in hyperprolactinemic patients (six out of seven). A much higher number of CFU-E colonies was observed in the four patients with a positive EPO-R message. We conclude from these data that abnormally high levels of PRL may increase the number of EPO-responsive hemopoietic precursors in vivo as they do in vitro. Since hyperprolactinemia associates in these patients with depressed EPO production, it may be regarded as a compensatory mechanism for the reduced availability of the hemopoietic factor.

Lipid mediators modulate the synthesis of interleukin 8 by human bone marrow stromal cells

Bone marrow stromal cells regulate marrow haematopoiesis by secreting interleukins (IL) such as IL-8. Lipid mediators modulate IL-8 synthesis in numerous cell types. We have investigated the effects of 5 lipid mediators (PAF, PGE(2), LTB(4), 12-HETE and 15-HETE) on the spontaneous and cytokine-induced IL-8 synthesis by human bone marrow stromal cells. By using reverse-transcriptase polymerase chain reaction (RT-PCR) we demonstrate that these cells constitutively express IL-8 transcripts. By using a specific ELISA, we found that the production of IL-8 by marrow stromal cells is enhanced after stimulation with 12-HETE (1 microM) both in serum-free and serum-containing culture medium. LTB(4)(1 microM) enhances IL-8 production only in serum-supplemented medium. PAF, PGE(2)and 15-HETE (1 microM to 0.1 nM) have no effect on the spontaneous and serum-induced production of IL-8 by human bone marrow stromal cells. PGE(2)(1 microM or 10 nM) reduces marrow stromal cell IL-8 synthesis in response to IL-1alpha or TNF-alpha. In contrast, PAF, 12-HETE, 15-HETE and LTB(4)have no effect. In conclusion, various lipid mediators modulate the spontaneous, serum- or cytokine-induced IL-8 synthesis by bone marrow stromal cells, highlighting, for the first time, their potential role in the regulation of IL-8 production within the human bone marrow.

Prolactin exerts hematopoietic growth-promoting effects in vivo and partially counteracts myelosuppression by azidothymidine

Prolactin (PRL) is a neuroendocrine hormone that influences immune and hematopoietic development. The mechanism of action of this hormone in vivo remains unclear; therefore, we assessed the effects of PRL on hematopoiesis in vivo and in vitro. Normal resting mice were treated with 0, 1, 10, or 100 microg of recombinant human prolactin (rhPRL) for 4 consecutive days and euthanized on the fifth day for analysis of myeloid and erythroid progenitors in the bone marrow and spleen. Both frequencies and absolute numbers of splenic colony-forming unit granulocyte-macrophage (CFU-GM) and burst-forming unit-erythroid (BFU-e) were significantly increased in mice receiving rhPRL compared to the controls that had received saline only. Bone marrow cellularities were not significantly affected by any dose of rhPRL, but the absolute numbers and frequencies of bone marrow CFU-GM and BFU-e were augmented by rhPRL. These results suggest that rhPRL can promote hematopoiesis in vivo. Because rhPRL augments myeloid development in vivo, we examined the potential of the hormone to reverse the anemia and myelosuppression induced by azidothymidine (AZT). Mice were given rhPRL injections concurrent with 2.5 mg/mL AZT in drinking water. rhPRL partially restored hematocrits in the animals after 2 weeks of treatment and increased CFU-GM and BFU-e in both spleens and bone marrow. The experiments with AZT and rhPRL support the conclusion that the hormone increases myeloid and erythroid progenitor numbers in vivo, and they suggest that the hormone is clinically useful in reversing myelosuppression induced by AZT or other myeloablative therapies.

Expression of platelet-activating factor receptor transcript-1 but not transcript-2 by human bone marrow cells

The presence of platelet-activating factor receptor (PAF-R) transcripts 1 and 2 was investigated in human bone marrow cells by a reverse transcriptase polymerase chain reaction (RT-PCR) procedure which detected their simultaneous presence. RT-PCR experiments reveal PAF-R transcript 1 (but not 2) in freshly isolated mononuclear marrow cells, CD34+ hematopoietic stem/progenitor cells and cultured marrow stromal cells. For these experiments, the 5637 human bladder carcinoma cell line is used as a positive control for the presence of PAF-R transcripts 1 and 2. Flow cytometry experiments confirm the presence of PAF-R on marrow stromal cells and CD34+ stem/progenitor cells. In conclusion, the expression of PAF-R transcript 1, which mainly exists in circulating leukocytes, is also found in CD34+ stem/progenitor cells and cells of the marrow microenvironment, strengthening the potential role of PAF during marrow hematopoiesis.

Neuroendocrine-induced synthesis of bone marrow-derived cytokines with inflammatory immunomodulating properties

Although cytokines and other soluble regulators of immunity are known to be involved in hematopoiesis, little is known about the signals that induce the synthesis of those mediators locally. Based on recent studies linking the neuroendocrine hormone thyrotropin [thyroid-stimulating hormone (TSH)] to immune cell function in other tissues, we investigated the capacity of TSH to activate cytokine responses from bone marrow cells. These studies reveal that stimulation of the TSH receptor on bone marrow cells-using highly purified or recombinant TSH or by direct stimulation with anti-TSH receptor antibodies-rapidly induces the synthesis of cytokines from bone marrow cells that are classically used in the regulation of inflammatory responses. Of 13 cytokines screened for activity by ELISA or by RNase protection assays for gene expression, IL-6, IFN-beta, TNFalpha, TNFbeta, TGFbeta2, and lymphotoxin-beta responses were reproducibly induced by TSH within 2-3 h of stimulation. Intracellularly, TSH stimulation of bone marrow cells caused rapid increases in cAMP levels and induced the phosphorylation of the Jak2 protein kinase, thereby defining a novel G-protein-coupled receptor/cytokine synthesis pathway. These findings demonstrate that TSH can serve as a primary inductive signal of cytokine production by bone marrow cells.