Immunomodulation by bromocriptine

Modulatory role of prolactin in type 1 diabetes

OBJECTIVES

Patients with type 1 diabetes mellitus have been reported to have elevated prolactin levels and a possible relationship between prolactin levels and the development of the disease has been proposed. However, some studies show that prolactin mediates beneficial functions in beta cells. Therefore, we review information on the roles of prolactin in type 1 diabetes mellitus.

CONTENT

Here we summarize the functions of prolactin in the immune system and in pancreatic beta cells, in addition, we describe studies related to PRL levels, its regulation and alterations of secretion in patients with type 1 diabetes mellitus.

SUMMARY

Studies in murine models have shown that prolactin protects beta cells from apoptosis, stimulates their proliferation and promotes pancreatic islet revascularization. In addition, some studies in patients with type 1 diabetes mellitus have shown that elevated prolactin levels correlate with better disease control.

OUTLOOK

Prolactin treatment appears to be a promising strategy to improve beta-cell vascularization and proliferation in transplantation and immunotherapies.

Prolactin and autoimmunity: The hormone as an inflammatory cytokine

Nowadays, more than 80 autoimmune disorders are recognized, in which an aberrant immune response against different organs and tissues plays a crucial role. Hormonal homeostasis has great influence in achieving competent and healthy immune system function. Prolactin has a bioactive function acting as a hormone and a cytokine. It influences the immune system modulation, mainly inhibiting the negative selection of autoreactive B lymphocytes. Hyperprolactinemia has been detected in many patients with different autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, Sjögren syndrome, multiple sclerosis, autoimmune thyroid disease, systemic sclerosis, among others, and its believed to play a crucial role in disease pathogenesis. A direct correlation between prolactin levels and disease activity was not clear. Genetic factors may have a role in humans as in animal models. Dopamine agonists have proven to offer clinical benefits among autoimmune patients and represent a promising therapy to be explored. In this review, the authors attempt to provide a critical overview on the role of prolactin in the immune system, exploring its contribution to the development of autoimmune diseases.

Prolactin, autoimmunity, and motherhood: when should women avoid breastfeeding?

The sexual dimorphic prevalence of autoimmunity represents one of the most alluring observations among the mosaic of autoimmunity. Sex hormones are believed to be a mainstay of this asymmetry. The greater prevalence of autoimmunity among fertile women, disease onset/relapses during pregnancy, and postpartum are some of the points that support this theory. Undeniably, motherhood represents one of the most remarkable challenges for the immune system that not only has to allow for the conceptus but also deal with extraordinary hormonal alterations. Prolactin has a recognized immune-stimulatory effect, mainly inhibiting the negative selection of autoreactive B lymphocytes. In accordance, hyperprolactinemia has been associated with several autoimmune diseases, interfering with its pathogenesis and activity. During the pregnancy and lactation period, assorted autoimmune patients experience relapses, suggesting an active interference from increased levels of prolactin. This association was found to be significant in systemic lupus erythematosus, rheumatoid arthritis, and peripartum cardiomyopathy. Furthermore, treatment with bromocriptine has shown beneficial effects specially among systemic lupus erythematosus patients. In this review, we attempt to provide a critical overview of the link between prolactin, autoimmune diseases, and motherhood, emphasizing whether breastfeeding should be avoided among women, both with diagnosed disease or high risk for its development.

Prolactin as immune cell regulator in Toxocara canis somatic larvae chronic infection

Toxocariasis is a zoonotic disease produced by ingestion of larval Toxocara spp. eggs. Prolactin (PRL) has been considered to have an important role in Toxocara canis infection. Recent evidence has found that PRL directly can increase parasite growth and differentiation of T. canis The present study, evaluated the effect of high PRL levels on the immune system's response and parasites clearance in chronic infection. Our results showed that hyperprolactinemia did not affect the number of larvae recovered from several tissues in rats. Parasite-specific antibody production, showed no difference between the groups. Lung tissue presented eosinophilic granulomas typical of a chronic infection in all the experimental groups. Flow cytometry analysis was made in order to determine changes in the percentage of innate and adaptive immune cell subpopulations in the spleen, peripheric (PLN) and mesenteric (MLN) lymphatic nodes. The results showed a differential effect of PRL and infection on different immune compartments in the percent of total T cells, T helper cells, T cytotoxic cells, B cells, NK cells, and Tγδ cells. To our knowledge, for the first time it is demonstrated that PRL can have an immunomodulatory role during T. canis chronic infection in the murine host.

Immunomodulatory Effects Mediated by Dopamine

Dopamine (DA), a neurotransmitter in the central nervous system (CNS), has modulatory functions at the systemic level. The peripheral and central nervous systems have independent dopaminergic system (DAS) that share mechanisms and molecular machinery. In the past century, experimental evidence has accumulated on the proteins knowledge that is involved in the synthesis, reuptake, and transportation of DA in leukocytes and the differential expression of the D1-like (D1R and D5R) and D2-like receptors (D2R, D3R, and D4R). The expression of these components depends on the state of cellular activation and the concentration and time of exposure to DA. Receptors that are expressed in leukocytes are linked to signaling pathways that are mediated by changes in cAMP concentration, which in turn triggers changes in phenotype and cellular function. According to the leukocyte lineage, the effects of DA are associated with such processes as respiratory burst, cytokine and antibody secretion, chemotaxis, apoptosis, and cytotoxicity. In clinical conditions such as schizophrenia, Parkinson disease, Tourette syndrome, and multiple sclerosis (MS), there are evident alterations during immune responses in leukocytes, in which changes in DA receptor density have been observed. Several groups have proposed that these findings are useful in establishing clinical status and clinical markers.

Periparturient immunosuppression and strategies to improve dairy cow health during the periparturient period

Common health problems observed during peripartum include milk fever, mastitis, fatty liver disease, ketosis, dystocia, retained placenta, metritis, hypomagnesaemia and abomasal displacements. The increased incidence of health problems observed during the periparturient period can be partly attributed to suboptimal immune responses. Factors contributing to decreased periparturient immunity include the act of parturition itself, impaired leukocytic activity, effects of colostrogenesis and lactogenesis, and associated hypocalcemia and negative energy balance. Nutritional and other management strategies represent a relevant short-term strategy aimed at improving the health and welfare of the transitioning cow. Additionally, it is important to consider improving the health of dairy herds through the genetic selection of animals with enhanced robustness by identifying those with superior disease resistance or resilience in the face of infection. As a consequence these animals are better able to cope with the production and environmental stresses. These may provide long-term selection strategies for improving the health and welfare of the transitioning cow particularly when combined with sound management practices, allowing dairy cattle to reach their full genetic potential.

Prolactin in combination with interferon-β reduces disease severity in an animal model of multiple sclerosis

Previous work has demonstrated that the hormone prolactin promotes oligodendrocyte precursor proliferation and remyelination following lysolecithin-induced demyelination of the mouse spinal cord. Prolactin, however, can elicit pro-inflammatory responses, and its use in the prototypical demyelinating and inflammatory condition, multiple sclerosis (MS), should thus be approached cautiously. Here, we sought to determine whether recombinant prolactin could alter the course of experimental autoimmune encephalomyelitis (EAE), an inflammatory animal model of MS. Consistent with previous literature, we found that prolactin activated leukocytes in vitro. Daily treatment with prolactin from around the time of onset of clinical signs, for 9 (days 9 to 17) or 25 (days 9 to 33) days did not increase clinical or histological signs of EAE over that of vehicle-treated mice. Instead, the combination of prolactin and a suboptimal dose of recombinant murine interferon-β resulted in (days 9 to 17 group) or trended towards (days 9 to 33 group), a greater amelioration of clinical signs of EAE, compared to either treatment alone or to vehicle controls. Histological analyses corroborated the clinical EAE data. These results suggest that prolactin may be beneficial when administered in combination with interferon-β in MS.

Thyroid autoimmunity in patients with hyperprolactinemia: an observational study

Objective : To establish whether there is a relationship between hyperprolactinemia and primary thyroid disorders, focusing on patients with autoimmune features. Materials and methods : The medical records of 100 patients with hyperprolactinemia (HPRL) were retrospectively examined. Records of thyroid ultrasonography (USG), basal serum levels of thyroid stimulating hormone, circulating free thyroxine, free triiodothyronine, antithyroglobulin (anti-Tg), and antithyroperoxidase (anti-TPO) antibodies were analyzed. In 100 control subjects, matched by age and gender with HPRL patients, thyroid USG, thyroid function tests (TFTs), and autoantibody panel were obtained. Results : The median PRL in patients was 93 ng/mL (range: 37-470). Twenty-five patients (25%) and 22 controls (22%) had positive anti-Tg and/or anti-TPO titers (P = 0.739). The median serum PRL was 98 (37-470) ng/mL in patients with positive thyroid autoantibodies, and 92 (40-470) ng/mL in patients who were negative (P = 0.975). Among the individuals with autoantibody positivity TFTs abnormalities were more frequent in HPRL patients (60%, out of 25 patients, 14 with subclinical hypothyroidism and one with hyperthyroidism) than in controls (9.1%, out of 22 patients, 2 with subclinical hyperthyroidism) (P < 0.001). Twenty-seven patients with HPRL and 31 controls had goiter (27 vs. 31%, P = 0.437). Forty-six patients (46%) and 50 (50%) controls had one or more of the features of thyroid disorder, which were goiter, positive thyroid autoantibody, and thyroid function abnormality (P = 0.888). Conclusion : HPRL may be associated with more severe thyroid dysfunction in patients with thyroid autoimmunity.

Regulation of intestinal morphology and GALT by pituitary hormones in the rat

Here, the effects of neurointermediate (NIL), anterior (AL), and total hypophysectomy (HYPOX) on ileal mucosa cells and gut-associated lymphoid tissue (GALT) are reported. Compared with the sham-operated (SHAM) rats, the villi height and goblet cells numbers were significantly decreased in all groups. Lamina propria area decreased in AL and HYPOX, but not in NIL animals. CD8(+) but not CD4(+) lymphocytes decreased in the HYPOX and NIL groups. Paneth cells did not change, while IgA cells, IgM cells, and secretory IgA were significantly decreased in all groups. NIL but not AL animals lost significant numbers of IgA cells and secretory IgA. In summary, pituitary hormones exert lobe-specific regulatory effects on the gut and on GALT.

Neuroimmune regulation in immunocompetence, acute illness, and healing

Adaptive immunocompetence is maintained by growth hormone (GH), prolactin (PRL), and vasopressin (VP). Innate or natural immunocompetence depends on cytokines, hormones (especially of the hypothalamus-pituitary-adrenal axis), and catecholamines. The acute phase response (APR, or acute febrile illness) is an emergency defense reaction whereby the adaptive, T cell-dependent, immune reactions are suppressed and the innate immune function is dramatically amplified. Infection and various forms of injury induce APR. Cytokines [interleukin (IL)-1beta, tumor necrosis factor-alpha, and IL-6] stimulate corticotropin-releasing hormone (CRH) and VP secretion and cause a "sympathetic outflow." Colony-stimulating factors activate leukocytes. CRH is a powerful activator of the pituitary adrenocortical axis and elevates glucocorticoid (GC) levels. Cytokines, GCs, and catecholamines play fundamental roles in the amplification of natural immune defense mechanisms. VP supports the APR at this stage. However, VP remains active and is elevated for a longer period than is CRH. VP, but not CRH, is elevated during chronic inflammatory diseases. VP controls adaptive immune function and stimulates adrenocorticotropic hormone (ACTH) and PRL secretion. PRL maintains the function of the thymus and of the T cell-dependent adaptive immune system. The ACTH-adrenal axis stimulates natural immunity and of suppressor/regulatory T cells, which suppress the adaptive immune system. VP also has a direct effect on lymphoid cells, the significance of which remains to be elucidated. It is suggested that VP regulates the process of recovery from acute illness.

Hormonal influences in multiple sclerosis

The function of hormones has expanded to include immunomodulation and neuroprotection in addition to their classic roles. The story of how hormones influence inflammation and neuron and glial function is being slowly unraveled. There is increasing evidence that estrogen, progesterone, and testosterone contain immune responses and influence damage repair in the nervous system. Hormones such as prolactin and vitamin D are being explored as immunomodulators and may influence diseases such as multiple sclerosis (MS) or may be used therapeutically to modulate the immune response. More recently identified hormones, such as leptin and gherlin, may also influence the course of disease. This chapter reviews some of the evidence that supports a role for hormones in MS.

Reproductive experience modifies dopaminergic function, serum levels of prolactin, and macrophage activity in female rats

Reproductive experience (RE), i.e. pregnancy and lactation, induces physiological changes in mammals. Recent data show that neuroimmune interactions are modulated by a diversity of events involving neurotransmitters and neuropeptides. These molecules, particularly dopamine (DA), were reported to mediate the relevant cross talk between immune and neuroendocrine systems. Moreover, DA-mediated regulation of leukocyte function is a reasonable approach to investigate the DA-operated regulatory switch for immune-competent cells, such as macrophages. Therefore, the goals of the present study were to determine the effects of RE on: (1) dopaminergic function through hypothalamic levels of DA, dihydroxyphenylacetic acid (DOPAC), homovanilic acid (HVA), serotonin (5-HT), and 5-hydroxyindole acetic acid (5-HIAA); (2) basal levels of circulating prolactin (PRL); and (3) activity of peritoneal macrophage (phagocytosis and oxidative burst). A total of 16 adult (200-250 g) female Wistar rats were used, divided in two groups: nulliparous and primiparous. Approximately 2-3 weeks after weaning pups from the primiparous group, both groups of rats were tested. The findings indicate that: (1) DOPAC concentrations, DOPAC/DA and HVA+DOPAC/DA ratios decreased in primiparous rats as compared to virgin rats, (2) primiparous rats showed significantly lower serum PRL levels, and (3) phorbol miristate acetate (PMA)-induced oxidative burst was decreased in peritoneal macrophage from primiparous rats as compared to virgin rats. To test the possible positive correlation between serum levels of PRL and the intensity of oxidative burst by peritoneal macrophage, an extra experiment was done with adult virgin female rats treated with domperidone, an antagonist of DA receptors. Domperidone-treated animals showed increased serum levels of PRL and simultaneous increase in peritoneal macrophage oxidative burst. Thus, suggesting an indirect participation of hyperprolactinemia, induced by this treatment in peritoneal macrophage activity of female rats. These results suggest that a previous RE can modulate the activity of dopaminergic hypothalamic systems, while decreasing PRL serum levels and the oxidative burst of peritoneal macrophage. The neurochemical and hormonal RE-induced changes correlate with the immune alterations.

The remission of rheumatoid arthritis during pregnancy

Rheumatoid arthritis (RA) is an autoimmune disease that is favorably influenced by pregnancy but relapses after delivery. A variety of circulating factors has been considered as candidates for inducing gestational improvement of RA; however, the factors/pathways responsible remain still elusive. This review discusses recent research on the effect of pregnancy on RA with a focus on immunregulation, cytokine secretion, HLA antigens, microchimerism, and innate immunity. The complex hormonal and immunological alterations of pregnancy may temporarily correct the disturbed immunregulation of RA.

Dopamine plasma membrane transporter (DAT) in rat thymus and spleen: an immunochemical and immunohistochemical study

The expression of the dopamine plasma membrane transporter (DAT) was investigated in rat thymus and spleen by immunochemical and immunohistochemical techniques. Antibodies raised against a peptide mapping near the amino terminus of DAT were bound to a single band of approximately 76 kDa in thymus and spleen membranes as well as in striatal and kidney membranes which were used as dopaminergic reference tissues. Reverse transcription-polymerase chain reaction analysis revealed that both thymus and spleen expressed DAT mRNA. Immunohistochemistry revealed in rat thymus a DAT immune reaction in the wall of arteries located in septa of connective tissue as well as in the medulla, with a reticular localization and an apparent negative reaction of thymocytes. In the spleen, DAT immunoreactivity was located primarily in the red-white pulp marginal zone, within small cells, likely corresponding to lymphocytes and in the wall of white pulp arteries. The presence of a dopamine transporter suggests that dopamine released in the lymphoid microenvironment may contribute to neuroimmune modulation. It cannot be excluded a different activity of dopamine in primary and secondary immune organs, such as maturation and selection of lymphocytes and activation of immune responses in the spleen.

Experimental allergic encephalomyelitis in pituitary-grafted Lewis rats

Treatment of susceptible rats with dopaminergic agonists that reduce prolactin release decreases both severity and duration of clinical signs of experimental allergic encephalomyelitis (EAE). To assess to what extent the presence of an ectopic pituitary (that produces an increase in plasma prolactin levels mainly derived from the ectopic gland) affects EAE, 39 male Lewis rats were submitted to pituitary grafting from littermate donors. Another group of 38 rats was sham-operated by implanting a muscle fragment similar in size to the pituitary graft. All rats received subcutaneous (s.c.) injections of complete Freund's adjuvant (CFA) plus spinal cord homogenate (SCH) and were monitored daily for clinical signs of EAE. Animals were killed by decapitation on days 1, 4, 7, 11 or 15 after immunization and plasma was collected for prolactin RIA. In a second experiment, 48 rats were immunized by s.c. injection of a mixture of SCH and CFA, and then received daily s.c. injections of bromocriptine (1 mg/kg) or saline. Groups of 8 animals were killed on days 8, 11 or 15 after immunization and plasma prolactin was measured. Only sham-operated rats exhibited clinical signs of the disease when assessed on day 15 after immunization. A progressive decrease in plasma prolactin levels was observed in pituitary-grafted rats, attaining a minimum 15 days after immunization, whereas plasma prolactin levels were increased during the course of the disease in sham-operated rats. Plasma prolactin levels were higher in pituitary-grafted rats than in sham-operated rats 1 day after immunization, but lower on days 7, 11 and 15 after immunogen injection. Further supporting a correlation of suppressed prolactin levels with absence of clinical signs of EAE, rats that were administered the dopaminergic agonist bromocriptine showed very low plasma prolactin levels and did not exhibit any clinical sign of EAE. These results indicate that low circulating prolactin levels coincide with absence of clinical signs of EAE in Lewis rats.

Spotlight on the role of hormonal factors in the emergence of autoreactive B-lymphocytes

Pathogenic autoimmunity requires a combination of inherited and acquired factors. In as much as hormones influence the sexual dimorphism of the immune system, it is possible that they can initiate or accelerate an autoimmune process, and contribute to gender-biased autoimmune disorders. Not only natural hormones, but also endocrine disruptors, such as environmental estrogens, may act in conjunction with other factors to override immune tolerance to self-antigens. In lupus, murine and human studies demonstrate that female sex hormones are implicated in disease pathogenesis. In the B cell compartment, both prolactin and estrogen are immunomodulators that affect maturation, selection and antibody secretion. Their impact may be based on their capacity to allow autoreactive B cells to escape the normal mechanisms of tolerance and to accumulate in sufficient numbers to cause clinically apparent disease. Both hormones lead to the survival and activation of autoreactive B cells, but they skew B cell maturation towards different directions, with prolactin inducing T cell-dependent autoreactive follicular B cells and estrogen eliciting T cell-independent autoreactive marginal zone B cells. Differential modulation of the cytokine milieu by hormones may also affect the development and activation of specific mature B cell subsets. This novel insight suggests that targeted manipulation of these pathways may represent a promising avenue in the treatment of lupus and other gender-biased autoimmune diseases.

Mucosal Immunity and Self-Tolerance in the Ocular Surface System

This paper articulates a new working hypothesis that explains many of the pathophysiological conditions described under the common rubric "dry eye" as altered states of mucosal immune regulation. A central principle of mucosal immune physiology is that the parenchymal tissues at the effector sites, i.e., the sites at which secretory antibodies are produced, maintain local signaling milieus that support differentiation of IgA+ plasmablasts and survival of IgA+ plasmacytes. These local signaling milieus also support robust regulatory networks that maintain tolerance to commensual microbes, benign antigens, and parenchymal autoantigens. The regulatory networks are mediated by cycles of interactions between successive generations of dendritic cells, which normally mature with tolerogenic functions, and regulatory T cells, which normally reinforce the system's ability to generate new tolerogenic dendritic cells. The systemic endocrine environment controls expression of the local signaling milieu in the mammary gland and in the prostate and male urethral glands. Emerging evidence indicates that the local signaling milieu in the lacrimal gland also is determined, in part, by the systemic endocrine environment. This working hypothesis suggests explanations for the excess incidence of Sjogren syndrome among women and for the mechanisms of several different immunophysiological states in addition to Sjogren syndrome that, like Sjogren syndrome, are associated with the classical symptoms and signs of dry eye. It also comprises a promising rationale for specific new approaches to therapy.

Abrogation of delayed type hypersensitivity response to Candida albicans produced by a molecular mimic of phosphorylated prolactin

The effects of two major forms of prolactin (PRL) were examined on delayed type hypersensitivity (DTH) responses to Candida albicans. Unmodified PRL (U-PRL) had no effect on the DTH response, whereas a molecular mimic of phosphorylated PRL (S179D PRL) significantly inhibited immune responses to this robust antigen. This effect of S179D PRL was not accompanied by gross alterations in splenic T cell numbers, CD4/CD8 ratios, or T and B cell activation markers, but did produce a decrease in splenocyte apoptosis. Using gld animals, Fas ligand (FasL) was implicated in the suppressive effects of S179D PRL. Circulating IgG1 and IgG2 antibody levels were increased in response to treatment with both forms of PRL, but the effects of S179D PRL were most pronounced. Cytokine changes in the popliteal lymph nodes specific to S179D PRL treatment showed an inhibition of pro-inflammatory cytokines. In conclusion, mice treated with a molecular mimic of phosphorylated prolactin showed a profound inhibition of DTH responses to Candida correlating with an absence of GM-CSF, IL-4, and IL-13 production and a marked reduction in IL-12p70 synthesis.

Cyclosporine and bromocriptine-induced suppressions of CYP3A1/2 and CYP2C11 are not mediated by prolactin

The purpose of this study was to determine if the suppression of hepatic CYP3A1/2 (cytochrome P450 3A1/2) and CYP2C11 (cytochrome P450 2C11) by cyclosporine is mediated by prolactin. Male intact rats were given subcutaneous doses of either 15 mg/kg/day of cyclosporine or 1 ml/kg/day of cyclosporine vehicle concomitantly with one of the following: 500 mg/kg prolactin, 1 ml/kg prolactin vehicle, 4 mg/kg bromocriptine, or 1 ml/kg bromocriptine vehicle for 14 days. Protein expressions were measured using Western blot analysis and activities were measured using an in vitro testosterone hydroxylation assay. The administration of prolactin did not significantly alter CYP3A1/2 protein expression. Hypoprolactinemia, produced by bromocriptine, caused a significant suppression of CYP3A1/2 activity levels when bromocriptine was administered alone and in combination with cyclosporine (P<0.001, P<0.05; respectively). However, the cause of the suppression by bromocriptine was likely not the result of lowering prolactin levels. Bromocriptine administration also lowered CYP2C11 protein expression and activity, while prolactin administration had virtually no effect on CYP2C11. Chronic cyclosporine administration caused a 140% increase in prolactin area under the curve (AUC) (P<0.001). Bromocriptine caused a significant decline in endogenous prolactin secretion, however, concurrent cyclosporine administration did not recover these levels. Overall, while both cyclosporine and bromocriptine, separately, can significantly alter the fate of hepatic P450 enzymes, the suppression is likely not due to an alteration in prolactin levels.

Prolactin as a modulator of B cell function: implications for SLE

Prolactin is not only a lactigenic hormone but also an immunomodulator involved in lymphocyte survival, activation and proliferation. There is increasing data implicating prolactin in autoimmunity, and specifically in SLE. Increased serum prolactin levels have been reported in lupus patients of both genders, and have been associated with accelerated disease expression and early mortality in lupus-prone mice. Furthermore, suppression of prolactin secretion with bromocriptine provides beneficial effects in murine lupus, and perhaps in some SLE patients as well. Treatment with prolactin that causes mild to moderate hyperprolactinemia, similar to that present in SLE patients, breaks tolerance and induces a lupus-like illness in non-spontaneously autoimmune mice with a susceptible genetic background. These immuno stimulatory effects of prolactin are mediated by a decrease in negative selection and the maturation of autoreactive B cells to the follicular subset. Consistent with the fact that follicular B cells are T cell dependent, CD4+ T cells are necessary for the prolactin-mediated break down of B cell tolerance. In mice, the effects of prolactin on the immune system are genetically determined, suggesting that only a subset of SLE patients are likely to have a prolactin-responsive disease. The manipulation of serum prolactin or, even more specifically, follicular B cells that are susceptible to the immuno stimulatory effects of prolactin, may provide novel therapeutic options for those SLE patients with a prolactin-modulated disease.

Prolactin enhances production of interferon-gamma, interleukin-12, and interleukin-10, but not of tumor necrosis factor-alpha, in a stimulus-specific manner

Prolactin, an anterior pituitary hormone, has been shown to have a role in immunomodulation. Some reports have shown the importance of prolactin in activating lymphocytes and macrophages, while in hyperprolactinemia patients, prolactin was found to decrease lymphocyte activation and natural killer function. In the present work, at physiological (15ng/ml) and stress-induced levels (30ng/ml) of prolactin, interferon-gamma (IFN-gamma) and interleukin (IL)-12 p70 levels, but not of IL-10 and tumor necrosis factor-alpha (TNF-alpha), increased significantly (p<0.05-0.006) in phytohemeagglutinin (PHA)+lipopolysaccharide (LPS)-stimulated whole blood. However, no such effect was observed at high concentrations of prolactin (100-300ng/ml). In addition, 15ng/ml of prolactin reversed hydrocortisone suppressive effect on IFN-gamma, IL-12 p70, and IL-10 production in PHA+LPS-stimulated whole blood. On the other hand, in LPS-stimulated whole blood, prolactin enhanced significantly (p=0.027) the production levels of IL-10, but not of IFN-gamma, IL-12 p70, and TNF-alpha, in non-concentration-dependent manner. These results suggest that prolactin modulates cytokine response during antigenic response, and this modulation is stimulus specific.

Prolactin and prolactin receptor gene polymorphisms in multiple sclerosis and systemic lupus erythematosus

Genes encoding for prolactin (PRL) and its receptor (PRLR) are possible candidates for multiple sclerosis (MS) and systemic lupus erythematosus (SLE) susceptibility. In fact: (1) a prolactin secretion dysfunction has been described in several autoimmune diseases including SLE and MS and their animal models; (2) both PRL and PRLR are structurally related to members of the cytokine/hematopoietin family and have a role in the regulation of the immune response; and (3) both PRL and PRLR genes map in genomic regions that showed linkage with autoimmunity. Prolactin maps on chromosome 6p, about 11-kb telomeric to HLA-DRB1 and PRLR in 5p12-13, which revealed evidence of linkage with MS in different populations. To evaluate a possible role of these two genes in SLE and MS we performed an association study of 19 PRL and PRLR single nucleotide polymorphisms (SNPs). These were directly searched by DHPLC in a panel of SLE and MS patients and selected from databases and the literature. The SNP allele frequencies were determined on patient and control DNA pools by primer-extension genotyping and HPLC analysis. Moreover a panel of HLA typed SLE and control individuals were individually genotyped for the PRL G-1149T polymorphism previously described to be associated with SLE. No statistically significant difference in the allele distribution was observed for any of the tested variations.

Anti-prolactin autoantibodies in paediatric systemic lupus erythematosus patients

The aim of this study was to determine the frequency of anti-prolactin autoantibodies and the relationship among anti-prolactin autoantibodies, serum prolactin (PRL) levels and lupus activity in paediatric patients with systemic lupus erythematosus (SLE) using a transversal study. One-hundred and three consecutive paediatric SLE patients were tested for serum anti-PRL autoantibodies and PRL levels. Clinical disease activity was scored using the SLEDAI index. Anti-PRL autoantibodies were measured by means of gel filtration. The frequency of anti-PRL autoantibodies was 6.7% (7/103), on the basis of the amount of immunoreactive PRL eluted in molecular weight fraction corresponding to IgG (150 kDa). No anti-PRL autoantibodies were found in normoprolactinaemic patients. By contrast, 21.8% (7/32) hyperprolactinaemic patients (hPRL) had anti-PRL autoantibodies. There was a correlation between anti-PRL autoantibody and serum levels of PRL (r(s) = 0.98, P = 0.0001). Lupus activity was present in 64/103 (62.1%) patients, without a significant difference in the frequency of anti-PRL autoantibodies when compared to inactive lupus (7.8 vs 5.1%, P > 0.05). Higher levels of serum PRL were associated with lupus activity regardless of other variables (39.6% vs 17.9%, P = 0.05). Patients with anti-PRL autoantibodies had higher levels of serum PRL than those without anti-PRL autoantibody (41.85 vs 17.77 ng/ml, P = 0.01) and significantly different frequency of hPRL (100 vs 26%, r = 0.4531, P < 0.001). We have identified a subset of paediatric SLE patients with hPRL and anti-PRL autoantibodies. Anti-PRL autoantibodies were associated with hPRL state and antibody titres correlated positively with serum PRL levels. These data suggest that anti-PRL autoantibodies could be responsible for hPRL in a subset of SLE patients. An increase in serum PRL levels proved to be related to lupus activity, but there was no statistical relationship between anti-PRL autoantibodies and lupus activity.

Analysis of anti-prolactin autoantibodies in systemic lupus erythematosus

Evidence has shown that prolactin is an essential component of an effective immune response. In systemic lupus erythematosus, clinical trials have produced controversial information about the role of PRL. Some results find association between serum PRL levels and disease activity. In contrast, other authors did not find this. Recently, autoantibodies against prolactin in SLE patients have been described. One hundred percent of SLE patients with anti-PRL autoantibodies had hyperprolactinemia (hPRL) and 31.7% of the SLE patients classified with idiopathic hPRL had anti-prolactin antibodies. A similar result was found in 103 pediatric SLE patients. The patients with idiopathic hyperprolactinemia and anti-PRL autoantibodies had less clinical and serological lupus activity than the SLE patients with idiopathic hyperprolactinemia, but without anti-PRL autoantibodies. This evidence suggests that anti-PRL autoantibodies or the complex with any other molecule, like macroprolactinemia (big-big PRL) could have attenuated biological activity and this could explain why some clinical studies did not find any association between serum PRL levels and disease activity in SLE patients. However, studies in vitro have shown normal or elevated biological activity in Nb2 cell lines using PRL from serum with anti-PRL autoantibodies from patients with or without autoimmune diseases. Several conclusions could be drawn. One is that while a set of hyperprolactinemic SLE patients display autoantibodies against PRL, it is not clear what role these autoantibodies play in the whole system. However, until now, we knew that the patients with antibodies to PRL lacked the clinical symptoms of hyperprolactinemia such as menstrual disturbances and/or galactorrhea and show less clinical and serological lupus activity.

Prolactin in murine systemic lupus erythematosus

Murine systemic lupus erythematosus (SLE) manifests several autoimmune perturbations that resemble human SLE, including cytokine aberrations, lymphoproliferation, hypergammaglobulinemia, autoantibody formation, and immune complex glomerulonephritis. In multiple studies, elevated serum prolactin concentrations (hyperprolactinemia) stimulated appearance or progression of murine lupus. Autoimmune disease acceleration by prolactin appears to be accentuated by estrogen stimulation of prolactin secretion and independent of immunosuppressive effects of androgens such as testosterone. Conversely, suppression of serum prolactin concentrations by bromocriptine inhibits development of murine SLE. These data clearly support the concept that prolactin is immunostimulatory in autoimmune disease and that the therapeutic goal of lowering serum prolactin concentrations may be beneficial to patients. Further utilization of murine SLE models will facilitate dissection of the actions and interactions of prolactin with estrogen, progesterone and testosterone and lead to a better understanding of hormonal immunomodulation and therapy of autoimmune disease.

Postnatal development of dopamine receptor expression in rat peripheral blood lymphocytes

Postnatal development in the expression of dopamine D1-like and D2-like receptors was investigated in peripheral blood lymphocytes of male Wistar rats aged 1, 3, 4, 8, 12 and 16 weeks of age by radioligand binding assay techniques. Sample of frontal cortex, striatum and hippocampus were also investigated as reference tissues. The dopamine D1-like receptor antagonist [3H]SCH 23390 and the dopamine D2-like receptor agonist [3H]7-OH-DPAT were used as radioligands. The affinity (K(d)) of [3H]SCH 23390 or of [3H]7-OH-DPAT binding was unchanged in lymphocytes of rats of different age groups. The density (B(max)) of [3H]SCH 23390 binding sites increased from the 1st to the 3rd week of age, remained constant from the 3rd to the 8th week of age, and then increased slightly at 12 and 16 weeks of age. The B(max) value of [3H]7-OH-DPAT binding to lymphocytes increased from the 1st to the 3rd week of age, remained constant from the 3rd to the 4th week, increased again until the 12th week and then plateaued. Dopamine D1-like and D2-like receptor maturation in frontal cortex, hippocampus and striatum revealed an increased receptor density until the 4th week of age and a relative stabilization of receptor density values between the 4th to the 12th week depending on the area considered. Comparatively postnatal maturation of lymphocyte dopamine D1-like receptors displayed a pattern different from that of brain areas investigated, whereas maturation of D2-like receptors displayed a pattern similar to that of striatum. The quantitative and/or qualitative dissimilarities between development of lymphocyte and brain dopamine receptors suggest that from a developmental point of view lymphocyte dopamine receptors probably cannot be considered as a marker of homologous brain receptors.

Enhanced serum prolactin (PRL) in patients with systemic lupus erythematosus: PRL levels are related to the disease activity

Recent accumulated evidence suggests that prolactin (PRL) is an important immunomodulator and plays a part in the pathogenesis of systemic lupus erythematosus (SLE). The current study assessed the frequency of hyperprolactinaemia in patients with SLE and its association with defined clinical manifestations or serological abnormalities. PRL levels were analysed in 60 patients with SLE including a follow-up of 20 patients, 18 patients with rheumatic autoimmune diseases other than SLE (AID) and in 47 normal healthy subjects (NHS) using ELISA. Clinical manifestations and disease activity (ECLAM) were recorded. Autoantibodies (anti-dsDNA, anti-CL) were determined by standard techniques. In all, 28.3% of the patients with SLE had raised serum PRL. Their PRL levels (17.4+/-15.1 ng/ml, P<0.0001) and those of patients with AID (13.1+/-10.3 ng/ml, P<0.001) were significantly higher compared to NHS (6.3+/-3.2 ng/ml). Anti-dsDNA (r(s) = 0.3, P = 0.04) and anti-CL antibody titres (IgG; r(s) = 0.3, P = 0.03) correlated with PRL level. Furthermore, elevated erytthrocyte sedimentation rate (ESR), anaemia, decrease in C3, fatigue, fever and renal involvement were associated with hyperprolactinaemia. These results were confirmed by follow-up examinations. Moderate hyperprolactinaemia is present in a subset of patients with SLE and serum PRL correlates with clinical and serological disease activity.

Bromocriptine in rheumatic and autoimmune diseases

BACKGROUND AND OBJECTIVES

Multiple lines of evidence support the concept that the anterior pituitary hormone prolactin has a pathogenic role in rheumatic and autoimmune diseases including, but not limited to, rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), Reiter's syndrome, psoriatic arthritis, and uveitis. Conversely, the dopaminergic agonist bromocriptine appears to have therapeutic effects through suppression of pituitary prolactin secretion and, perhaps, through actions on peripheral dopamine receptors. This article reviews the experimental and clinical data supporting the therapeutic use of bromocriptine as a nonstandard or adjunctive therapy in rheumatic and autoimmune diseases.

METHODS

Data addressing the potential therapeutic role of bromocriptine in rheumatic and autoimmune diseases, as well as frequently associated comorbidities, was accumulated from the author's work, online literature search of the National Library of Medicine, and references from these identified publications.

RESULTS

There have been a number of clinical therapeutic trials using 2.5 to 30 mg of bromocriptine per day in a single or divided dose, which have shown efficacy with minimal side effects in the treatment of rheumatic and autoimmune diseases. In RA, bromocriptine administration has induced immunosuppression of several immune parameters and has been associated with improvements in morning stiffness, grip strength, numbers of swollen/painful joints, and the Health Assessment Questionnaire disability index. In two blinded studies, bromocriptine reduced the number of SLE flares and was as effective as hydroxychloroquine in reducing lupus disease activity indices, respectively. In case reports, bromocriptine has been used successfully in the treatment of Reiter's syndrome enthesopathy and psoriatic arthritis. The potential efficacy of bromocriptine in the treatment of uveitis and multiple sclerosis is suggested but remains to be verified.

CONCLUSIONS

Double-blind, placebo-controlled studies are limited, but clinical observations and trials support the use of bromocriptine as a nonstandard primary or adjunctive therapy in the treatment of recalcitrant RA, SLE, Reiter's syndrome, and psoriatic arthritis and associated conditions unresponsive to traditional approaches. Additional investigation is needed to verify this conclusion and extend preliminary results.

RELEVANCE

In patients with rheumatic and autoimmune diseases, bromocriptine may be a relatively safe and efficacious alternative therapy. Semin Arthritis Rheum 31:21-32.

Identification of dopamine plasma membrane and vesicular transporters in human peripheral blood lymphocytes

Plasma membrane dopamine transporter (DAT), vesicular monoamine transporters (VMAT) type-1 and -2 and the expression of the dopaminergic markers dopamine and tyrosine hydroxylase were assessed in membranes and/or in cytospin centrifuged human peripheral blood lymphocytes. The radiolabeled DAT ligand [3H]GBR12935 was bound to peripheral lymphocytes in a manner consistent with the specific binding to a dopamine uptake system, with a dissociation constant similar to that found in striatum, but with a lower density of binding sites. On the other hand, no specific binding occurred in cerebellum used as a test tissue not expressing DAT. Western blot analysis using antibodies raised against amino or carboxy terminus of DAT or against VMAT-1 or VMAT-2 revealed labeling of single bands of approximately 76, 55 or 68 KDa, respectively, displaying similar migration characteristics in lymphocytes and test tissues used for comparison. Immunofluorescence revealed that anti-dopamine, anti-tyrosine hydroxylase, anti-DAT, anti-VMAT-1 and anti-VMAT-2 antibodies labeled the total population of cytospin-centrifuged lymphocytes mounted on microscope slides. Confocal laser microscopy demonstrated that dopamine and VMAT-2 immunoreactivity was developed mainly in cytoplasmic punctiform areas likely corresponding to vesicles and to a lower extent was associated to plasma membrane. Tyrosine hydroxylase immunoreactivity was diffused to cytoplasm and to plasma membrane of lymphocytes, whereas DAT and VMAT-1 immunoreactivity were located almost exclusively in lymphocyte plasma membrane and cytoplasm, respectively. Lymphocyte DAT characterized in this study has probably functional relevance as [3H]dopamine was taken up by intact lymphocytes and uptake was inhibited specifically by compounds known to affect dopamine transport. These findings indicate that human peripheral blood lymphocytes possess DAT plasma membrane and VMAT-1 and VMAT-2 transporters. Increasing evidence indicates that dopamine transporter changes may be related to neuronal injury. In view of this assessment of lymphocyte DAT and VMAT transporters can be considered for identifying pathologies characterized by impaired dopaminergic neurotransmission.

Estrogen, prolactin, and autoimmunity: actions and interactions

Estrogen and prolactin have a reciprocal endocrinologic relationship and both hormones have pleiotropic effects on the immune system. Despite the presence of a number of confounding variables, these hormones modulate autoimmunity; however, mechanisms by which this modulation occurs remain obscure. Estrogen appears to suppress cell-mediated and augment humoral-based immunity. Prolactin appears to stimulate both cell and humoral-based immunity. Both hormones have been shown to modulate IFN gamma secretion. Similar evidence in experimental models, human autoimmune disease, and during pregnancy in autoimmune disease patients suggests disparate effects of estrogen and prolactin on autoimmune responses and disease pathogenesis. In the NZB x NZW F1 mouse model of lupus, prolactin accelerates disease expression, whereas estrogen, devoid of its prolactin stimulating properties, is immunosuppressive and inhibits IL-2 production. Estrogen, because of its endocrinologic and immune effects, may directly or indirectly stimulate or inhibit immune responses. These dichotomous effects have limited its successful pharmacologic manipulation in human autoimmune disease with estrogen compounds, tamoxifen, oral contraceptives, antigonadotropic agents, or ovulation induction regimens. In contrast, reduction of immunostimulatory concentrations of prolactin with bromocriptine has successfully suppressed development or expression of murine and human autoimmune disease. Further investigation into actions and interactions of estrogen and prolactin with autoimmunity will provide a better understanding of the female preponderance of autoimmunity and facilitate a more rational approach to hormonal immunotherapy.

Prolactin enhances the in vitro production of IgG in peripheral blood mononuclear cells from patients with systemic lupus erythematosus but not from healthy controls

OBJECTIVES

Recent evidence suggests that prolactin (PRL) plays a part in the pathogenesis of systemic lupus erythematosus (SLE). Because B cell hyperreactivity and autoantibodies are characteristic hallmarks of SLE, this study aimed at assessing the impact of this pituitary hormone on IgG production by stimulating peripheral blood mononuclear cells (PBMC) with PRL.

METHODS

PBMC from 11 patients with SLE assessed by the ECLAM score and eight healthy controls were incubated with PRL and cultured for seven days. IgG production was measured by enzyme linked immunosorbent assay (ELISA).

RESULTS

Spontaneous IgG production of SLE PBMC was significantly enhanced compared with that found in healthy controls. After PRL stimulation, the IgG concentrations of supernatants from SLE PBMC were significantly higher than those of unstimulated PBMC (median 394 ng/ml). Of note, the physiological concentration of PRL (20 ng/ml) induced IgG production more effectively (median 1139 ng/ml) than PRL at 100 ng/ml (median 1029 ng/ml). In contrast, preincubation with PRL did not stimulate IgG production in normal PBMC. A significant correlation between PRL induced IgG production and the disease activity (ECLAM) of the patients with SLE was seen. Moreover, the maximum amount of PRL induced IgG depended on the serum PRL concentrations of the patients with SLE.

CONCLUSIONS

The results suggest that PBMC from patients with SLE have an extraordinarily high susceptibility to PRL, showing the most striking effect at a concentration usually found in vivo. This indicates a potential role for mild hyperprolactinaemia in the pathogenesis of SLE, influencing both IgG production and disease activity.

Anti-inflammatory effects of ergotamine in steers

The objective of this experiment was to investigate whether the ergot alkaloid, ergotamine (ET), an alkaloid used to model fescue toxicosis in cattle, modifies the response of cattle to endotoxin (LPS) challenge. Steers (n = 16) were divided into the following treatment groups: control (C), ergotamine (ET), endotoxin (LPS), and ET + LPS. ET and ET + LPS groups received a single bolus intravenous injection of ET (40 microg. kg. body wt(-1)), whereas C and LPS steers received a single bolus injection of sterile vehicle. Thirty minutes after ET/vehicle administration, a single bolus intravenous injection of LPS (0.2 microg. kg. body wt(-1)) was given. Blood was collected at various time points for 48 hr post. Endotoxin increased rectal temperature (RT) and the circulating levels of tumor necrosis factor-alpha (TNF-alpha), cortisol, haptoglobin (Hp), thromboxane B(2) (TXB(2)). The circulating Hp, TNF-alpha, and TXB(2) increases were blunted by pretreatment with ET compared with ET + LPS. Ergotamine by itself increased circulating cortisol and RT, whereas it decreased serum prolactin (PRL). Therefore, whereas administration of LPS at 0.2 microg/kg to steers resulted in an expected response, the combination of ET + LPS attenuated major effects of LPS alone. Thus, acute administration of ET appeared to be anti-inflammatory as it decreased the inflammatory response to LPS, an effect likely driven at least in part by the ET-caused cortisol increase.

Prolactin: structure, function, and regulation of secretion

Prolactin is a protein hormone of the anterior pituitary gland that was originally named for its ability to promote lactation in response to the suckling stimulus of hungry young mammals. We now know that prolactin is not as simple as originally described. Indeed, chemically, prolactin appears in a multiplicity of posttranslational forms ranging from size variants to chemical modifications such as phosphorylation or glycosylation. It is not only synthesized in the pituitary gland, as originally described, but also within the central nervous system, the immune system, the uterus and its associated tissues of conception, and even the mammary gland itself. Moreover, its biological actions are not limited solely to reproduction because it has been shown to control a variety of behaviors and even play a role in homeostasis. Prolactin-releasing stimuli not only include the nursing stimulus, but light, audition, olfaction, and stress can serve a stimulatory role. Finally, although it is well known that dopamine of hypothalamic origin provides inhibitory control over the secretion of prolactin, other factors within the brain, pituitary gland, and peripheral organs have been shown to inhibit or stimulate prolactin secretion as well. It is the purpose of this review to provide a comprehensive survey of our current understanding of prolactin's function and its regulation and to expose some of the controversies still existing.

The roles of prolactin, growth hormone, insulin-like growth factor-I, and thyroid hormones in lymphocyte development and function: insights from genetic models of hormone and hormone receptor deficiency

An extensive literature suggesting that PRL, GH, IGF-I, and thyroid hormones play an important role in immunity has evolved. Because the use of one or more of these hormones as immunostimulants in humans is being considered, it is of critical importance to resolve their precise role in immunity. This review addresses new experimental evidence from analysis of lymphocyte development and function in mice with genetic defects in expression of these hormones or their receptors that calls into question the presumed role played by some of these hormones and reveals unexpected effects of others. These recent findings from the mutant mouse models are integrated and placed in context of the wider literature on endocrine-immune system interactions. The hypothesis that will be developed is that, with the exception of a role for thyroid hormones in B cell development, PRL, GH, and IGF-I are not obligate immunoregulators. Instead, they apparently act as anabolic and stress-modulating hormones in most cells, including those of the immune system.

Dopamine, a neurotransmitter, influences the immune system

Dopamine (DA) is a monoamine neurotransmitter of both central and peripheral nervous system. Its role in the neural-immune communication has been discussed in the present review. Results reveal that in vivo damage or stimulation of specific central dopaminergic system suppresses or enhances functional activities of the immune effector cells. The possible influences of other immunomodulators of the brain by altering brain DA may be the underlying mechanism. Direct effects of DA on the immune effector cells are also contradictory, it is suppressive in vitro, while in pharmacological doses, it is mostly stimulatory in vivo. The possible mechanisms have been discussed. Lastly, future areas of relevance on DA and immunity have been highlighted to advance our knowledge regarding DA as an immune regulator.

Suppression of adjuvant arthritis in rats with chronic bromocriptine treatment does not prevent associated oxidative stress

We studied the effect of prolactin (PRL) inhibition by bromocriptine (BRC) in the first phase of adjuvant induced arthritis (AA), up to day 11(BRCl-AA), and in the whole time course of AA, up to day 23 (BRC-AA), on the development of the disease in male Lewis rats. On day 24, arthritic rats showed inhibition of PRL secretion, but not PRL mRNA expression in adenopituitaries. BRC treatment suppressed PRL serum levels and PRL mRNA expression in adenopituitaries. In BRC/-AA group PRL levels and PRLmRNA were at the level of rats with AA. Serum corticosterone (CORT) was stimulated by AA from 16.9+/-5.8 to 59.1+/-8.7 ngml(-1), p<0.05, to the same level in BRC-control (BRC-C) and BRC-AA group and further potentiated in BRCI-AA group (148.2+/-33.1 ngml(-1), p<0.05 vs. group with AA). Hind paw swelling was reduced but not completely inhibited in BRC1-AA group and totally prevented in BRC-AA rats as was the core temperature (36.5+/-0.1 degrees C vs. 37.4+/-.0.1 degrees C in AA rats on day 23, p<0.01). Serum concentration of NO-ZNO-3 rose in rats with AA to 28.7+/-2.5 &mgr;mo1L-1 against. 13.9+/-1.9 &mgr;molL(-1) in controls (p<0.01), remained elevated in BRC-AA group and was potentiated in BRC1-AA group (48.2+/-3.5 &mgr;mol(-1), p<0.01 vs. AA or BRC1-AA group) Thiobarbituric acid reactive substances (TBARS) and antioxidant capacity in the spleen were enhanced in rats with AA and to the same extent in BRC-AA or BRC1-AA groups. These results show a discrepancy between the suppression of clinical symptoms and persisting oxidative stress in AA rats after the BRC induced PRL inhibition. The potentiation of nintric oxide (NO-) production after the sudden cessation of PRL inhibition during the disease may promote further joint damage.

The expression of interleukin-6 (IL-6), IL-6 receptor, and gp130-kilodalton glycoprotein in the rat decidua and a decidual cell line: regulation by 17beta-estradiol and prolactin

The cytokine interleukin 6 (IL-6), a major mediator of immune and acute phase responses of the liver, has been implicated in the termination of pregnancy once expressed in the uterus. This study was undertaken to investigate the expression and regulation of genes encoding IL-6 and IL-6 receptor (IL-6R) in rat decidual tissue. Total RNA obtained from rat decidual tissue on different days of pseudopregnancy was analyzed by RT-PCR using specific primers for IL-6, IL-6R, and 130-kDa glycoprotein (gp130). Ribosomal L19 primers served as an internal control. IL-6R and gp130 were found to be expressed in the decidua throughout development, while no messenger RNA (mRNA) for IL-6 was detected. Interestingly, within several hours of culture, decidual explants acquired the ability to express IL-6. The apparent ability of decidual cells to express IL-6 and its lack of expression in vivo led us to examine whether the IL-6 gene is actively inhibited. Primary decidual cells were cultured in the presence of estradiol, progesterone, or PRL. Progesterone showed no effect, whereas estradiol and PRL reduced the level of IL-6 mRNA expression. To examine the mechanism by which these hormones inhibit IL-6 expression, we used a simian virus 40-transformed decidual cell line (GG-AD), which expresses only estrogen receptor-beta (ERbeta). Like primary decidual cells in culture, GG-AD cells express IL-6, IL-6R, and gp130 mRNA. When cultured in the presence of estradiol (0-100 ng/ml), mRNA for IL-6 and its receptor components were down-regulated in a dose-dependent manner. Estradiol also caused a dose-dependent decrease in IL-6 protein secretion into the culture medium. The inhibitory effect of estradiol on IL-6 mRNA expression was reversed by the antiestrogen ICI-164,384. Similar inhibition of IL-6 and gp130 mRNA expression was observed with PRL treatment. However, PRL had no effect on IL-6R mRNA levels. PRL inhibition of IL-6 expression was totally reversed by tyrphostin AG490, a JAK2 inhibitor. In summary, the results of this investigation indicate that IL-6 expression, which is detrimental to the maintenance of pregnancy, is inhibited in the rat decidual tissue. This inhibition is induced by PRL and estradiol, which down-regulate not only IL-6 expression, but also the expression of IL-6 receptor and signaling proteins. The results also suggest that PRL signaling to the IL-6 gene is mediated through the long form of PRL receptor and involves JAK2 activation, whereas that of estradiol can be transduced by estrogen receptor-beta.

Immune System Development and Function in Prolactin Receptor-Deficient Mice

Prolactin (PRL) is the primary lactogenic pituitary hormone that plays an essential role in many aspects of reproduction, from fertilization to mammary gland development and maternal behavior. PRL has also been reported to play a role in immunoregulation. Because initial observations indicated that hypophysectomized rats present abnormalities of the immune system, including increased thymic atrophy and lymphopenia, a number of studies have focused on the potential immunomodulatory roles of PRL. This hormone exerts its biological activities following binding to specific cell surface PRL receptors (PRLRs). In this report, we have characterized the development and function of the immune system in PRLR-deficient mice. Compared with wild-type control mice, PRLR−/− mice demonstrate no alterations in thymic or splenic cellularity or in the composition of the lymphocyte subsets present in primary (bone marrow and thymus) or secondary (spleen and lymph nodes) lymphoid organs. Lymphocytes from PRLR−/− mice are functional in vitro, as they can proliferate normally to mitogens, cytokines, and allogeneic cells. PRLR−/− splenocytes display normal NK-mediated cytotoxicity to YAC-1 target cells. In vivo studies have revealed that PRLR−/− mice are able to 1) generate normal steady-state Ig levels, 2) mount a normal specific Ig response following immunization with a T-dependent Ag, 3) eliminate injected allogeneic tumor cells, and 4) effectively control Listeria monocytogenes infection. Taken together, these results show that immune system development and function proceed normally in the absence of PRL-mediated signaling and suggest that PRLR pathways are not essential for immunomodulation in vivo.

Effects of haloperidol on the expression of lymphocyte dopamine receptor mRNAs in the rat

1. Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to investigate the effects of haloperidol treatment (1 mg/kg/day for 2, 7 or 21 consecutive days) on the expression of D1B and D3 dopamine receptor mRNAs in the rat lymphocytes. 2. The expression of D1B receptor mRNA was significantly decreased after 2 days of treatment and progressively returned toward basal values at the end of treatment. Conversely, haloperidol failed to modify the expression of lymphocyte D3 receptor mRNA. 3. These results indicate short-lasting dynamic changes of expression of lymphocyte D1B dopamine receptor mRNA by haloperidol and suggest that the effects of dopamine and dopaminergic drugs on the immune system might be mediated, at least in part, by direct interaction of these substances with dopamine receptors on lymphocyte membrane.

Prolactin and neuroimmunomodulation: in vitro and in vivo observations

Prolactin (PL) is a mammotropic neuropeptide produced by the pituitary and extrapituitary cells existing as several isoforms and belongs to the growth and lactogenic hormone family, which includes growth hormone and placental lactogens. The secretion of pituitary PL is under hypothalamic control. The cytokines IL-1, IL-2, and IL-6 also stimulate production, while IFN-gamma and endothelin-3 are inhibitory. PL exerts its effects via PL receptors (PLr) which exist as three isoforms. PL regulates reproduction, osmoregulation, and behavior and has potent immunomodulatory effects. PL is structurally related to members of the cytokine/hematopoietic family such as erythropoietin, GM-CSF, growth hormone, and IL-2 to IL-7. The PLr is a member of the cytokine/hematopoietic receptor family. Interaction of PL with PLr activates the Jak kinases which phosphorylate latent STAT proteins resulting in the activation of transcription. PL counteracts the effects of corticosteroids by enhancing Th1 cellular responses. Perturbations of PL physiology have significant immunologic effects. Hypoprolactinemia impairs immune function while hyperprolactinemia enhances active systemic lupus erythematosus, Reiter's disease, juvenile and adult rheumatoid arthritis (RA), autoimmune thyroiditis, multiple sclerosis, and cardiac allograft rejection. PL gene polymorphisms have now been shown to be linked to RA. Thus, manipulation of PL may have significant clinical utility. Further study of the relationship of the PL/PLr complex, other hormones, and the immune system will provide further insights into the potential therapeutic utility of this complex in immune diseases.

Dopamine D2-like receptors on human peripheral blood lymphocytes: a radioligand binding assay and immunocytochemical study

1. Peripheral blood lymphocytes express dopamine D1-like and D2-like receptors which were investigated using radioligand binding assay and molecular biology techniques. Analysis of dopamine D2-like receptors expressed by human peripheral blood lymphocytes with radioligand binding assay may offer a rapid technique for assessing receptor changes in disorders characterized by involvement of the dopaminergic system. However, the suitability of radioligand binding assay techniques to measure dopamine D2-like receptors is questioned. 2. In view of the discrepancy between data of dopamine D2-like receptor determination with molecular biology and radioligand binding assay techniques, we have assayed dopamine D2-like receptors expressed by human peripheral blood lymphocytes using as radioligands the dopamine receptor agonist 7-[3H]-hydroxy-N,N-di-n-propyl-2-aminotetraline ([3H]-7-OH-DPAT) and two antagonists ([3H]-spiperone and [3H]-nemonapride). 3. Analysis of saturation curves revealed a concentration-dependent binding of all compounds to human peripheral blood lymphocytes. Dissociation constant (Kd) values averaged between 0.15 and 0.40 nM for different radioligands. The maximum density of binding sites (Bmax) was low, ranging from 4.15 +/- 0.05 fmol/10(6) cells with [3H]-spiperone and 8.66 +/- 0.04 fmol/10(6) cells with [3H]-7-OH-DPAT. 4. Displacement curves of [3H]-7-OH-DPAT, [3H]-spiperone and [3H]-nemonapride binding to human peripheral blood lymphocytes revealed, using radioligand concentrations giving the highest specific:non-specific binding ratio, a pharmacological profile consistent with the labelling of dopamine D2-like receptors. The use of higher radioligand concentrations resulted in a poorly displaceable and characterizable binding. 5. Detection of dopamine D2, D3 and D4 receptor immunoreactivity in cytospin centrifuged peripheral blood lymphocytes revealed dopamine D3 and D4 but not D2 receptor immunostaining. 6. The above findings indicate in agreement with molecular biology studies, that dopamine D2-like receptors expressed by human peripheral blood lymphocytes belong to the D3 and D4 receptor subtypes. These receptors are detectable using either dopamine D2-like receptor agonists and antagonists as radioligands if controlled experimental conditions are followed. The standardisation of immunocytochemical techniques for detecting human peripheral blood lymphocyte dopamine receptors may contribute to clarify their role in lymphocyte function or as a peripheral marker of the status of the dopaminergic system.

Prolactin secretion is increased in patients with multiple sclerosis

Before the onset and during experimental allergic encephalomyelitis (EAE), the animal counterpart of multiple sclerosis (MS), prolactin levels were found to be elevated and bromocriptine was found to attenuate the attacks. This study was designed to determine whether patients with MS show evidence of hyperprolactinemia. Twelve patients with MS and twelve healthy controls were studied at baseline and with TRH stimulation, a provocative test for prolactin secretion. Compared to matched controls, patients with MS had slightly but significantly higher prolactin levels at baseline (10.2+/-1.6 vs 6.4 4+/-0.57 ng/ml, P=0.042), however, values were within the normal range. The prolactin levels post TRH were significantly higher in patients with MS: peak prolactin level was higher in patients than controls (57.08+/-6.144 vs 32.94+/-4.92 ng/ml, P=0.006). The area under the curve of prolactin was also higher in patients than in controls (3421.87+/-394.53 vs 2317.62+/-257.22 ng/ml, P=0.030). These findings are compatible with data from studies of experimental animals with MS and suggest that prolactin may play a role in the immunology of MS.

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.

Requirement of PI3-kinase activity for the nuclear transport of prolactin in cloned murine T lymphocytes

The murine T-cell clone, L2, requires both IL2 and PRL to proliferate. Proliferation and selected IL2-driven gene expression are blocked by treatment with rapamycin. Since prolactin translocation to the nucleus is IL2 dependent and required for proliferation, experiments were performed to identify activation pathways that might be involved in nuclear transport and proliferation. L2 cells were stimulated with IL2 in the presence and absence of the mTOR inhibitor rapamycin, PI3-kinase inhibitors (wortmannin, LY294002), the p38 MAP kinase inhibitor SB203580 and the vitamin D analog calcipotriol. The immunosuppressant rapamycin markedly inhibited IL2-induced proliferation and prolactin translocation to the nucleus. Similarly, wortmannin and LY294002 inhibited IL2-induced proliferation and markedly decreased the amount of prolactin transported to the nucleus. SB203580 and calcipotriol partially inhibited IL2-induced proliferation but had no effect on prolactin translocation. None of the inhibitors affected Lucifer Yellow uptake indicating that rapamycin, wortmannin and LY294002 did not inhibit early endosomal formation but rather worked to inhibit prolactin translocation at a later point in the retrograde transport pathway.

Use of neuroendocrine hormones to promote reconstitution after bone marrow transplantation

A survey of the previous literature and the data shown here indicate that neuroendocrine hormones such as growth hormone and prolactin may be of potential clinical use after bone marrow transplantation (BMT) to promote hematopoietic and immune recovery. The amounts of hormones used in our model do not promote weight gain suggesting that their lymphohematopoietic actions were independent of their anabolic effects. While the hormones may not produce the same extent of immune/hematopoietic effects when compared to conventional hematopoietic and immune stimulating cytokines (i.e. IL-2 or G-CSF), their pleiotropic effects and limited toxicity after systemic administration makes them attractive to test in the post-BMT setting. However, more work needs to be performed to understand the mechanism(s) of their action, particularly with regard to T-cell function and development.

Bromocriptine in systemic lupus erythematosus: a double-blind, randomized, placebo-controlled study

The objective of this study was to investigate the efficacy and safety of bromocriptine (BRC) as an adjunct to conventional treatment in systemic lupus erythematosus (SLE). A prospective, double-blind, randomized, placebo-controlled study compared BRC at a fixed daily dosage of 2.5 mg with placebo. Patients were followed for 2-17 months (mean 12.5 months). Disease activity was assessed using the SLE Disease Activity Index (SLEDAI), numbers of flares were recorded, and serum prolactin (PRL) levels were obtained at intervals during the study. Patients were allowed to take prednisone and immunosuppressive drugs. Sixty-six patients with SLE entered the study. Thirty-six were treated with BRC, and 30 controls received placebo. Sixteen patients were removed from the study during the treatment period: five in each group left the study because of adverse effects, five became pregnant, and one patient who took placebo died with central nervous system lupus. Four patients in the BRC treatment group and three patients in the placebo group moved away or stopped coming for study visits for unknown reasons, and were lost to follow-up during the course. At entry, serum PRL was (mean+/-s.d.) 24.8 ng/ml+/-18.4 in the BRC treatment group. This value fell to 5.8+/-9.0 after 12 months of treatment. Corresponding PRL values in controls were 23.7+/-22.1 pretreatment and 20.3+/-14 after 12 months. PRL levels in BRC-treated subjects were significantly lower than levels in control subjects after 3, 6, 9, and 12 months of treatment. The SLEDAI score on the fifth protocol visit was decreased significantly in the BRC group vs controls: 0.9+/-1.4 vs 2.6+/-4.5 (P < 0.05). Although the absolute number of flares in each group was similar, the mean number of flares/patient/month was decreased significantly in the BRC group compared to the control group (0.08+/-0.1 vs 0.18+/-0.2, P = 0.03). Long term treatment with a low dose of BRC appears to be a safe and effective means of decreasing SLE flares in SLE patients.

Differential effects of estrogen and prolactin on autoimmune disease in the NZB/NZW F1 mouse model of systemic lupus erythematosus

Estrogen and prolactin have been shown to modulate autoimmunity in the NZB/NZW F1 (B/W) mouse model of systemic lupus erythematosus (SLE). However, estrogen stimulates prolactin secretion. The goal of this study was to examine differential effects of estrogen and prolactin in the female B/W mouse model of SLE. B/W females were manipulated to create combinations of low and high concentrations of serum estrogen and prolactin. Hyperprolactinemic mice with either low or high serum estrogen levels had accelerated development of albuminuria at 24 and 32 weeks of age compared to normal and hypoprolatinemic mice. High estrogen/high prolactin mice also had a higher percentage of anti-DNA antibodies compared to mice in the low estrogen/low prolactin and the high estrogen/low prolactin groups. IgG levels were not significantly different between groups. Mean survival was shortest in the high estrogen/high prolactin group (34+/-1.0 weeks) and longest in the high estrogen/low prolactin group (42+/-1.2 weeks; P < 0.05). High levels of serum estrogen were associated with depressed in vitro lymphoproliferation and IL-2 production. This study suggests that high prolactin levels in either high or low serum estrogen states are associated with accelerated autoimmunity in the B/W mouse. This study further demonstrates that high estrogen levels do not accelerate murine SLE when the prolactin-stimulating property of estrogen is suppressed by bromocriptine. Further investigation of hormonal interactions in autoimmunity will provide a better understanding of hormonal immunoregulation and, perhaps, lead to improved clinical application of hormonal immunomodulation.