Analysis of anti-prolactin autoantibodies in systemic lupus erythematosus

Analysis of molecular heterogeneity of prolactin in human systemic lupus erythematosus

Hyperprolactinemia without clinical manifestations has been reported in some patients with systemic lupus erythematosus (SLE) because an increase of prolactin (PRL) is produced due to the BIG/BIG molecular variant (molecular variant, 150 kD). This research project aimed to determine levels of PRL: its bioactive form, the little nonglycosylated form (NGPRL) and variants with decreased bioactivity such as the BIG/BIG and the little glycosylated (GPRL), in 29 women and five men with SLE. PRL was assayed by IRMA with a kit from Immunotech Laboratory, the BIG/BIG form by precipitation with polyethyleneglycol 6000, and the NGPRL and GPRL by chromatography on Concanavalin-A-Sepharose. Increased PRL was detected in seven patients (20.6%) of whom three had increased BIG/BIG, six had increased GPRL and only four had increased NGPRL. The three cases with increased BIG/BIG were contrasted by chromatography on Sephadex G-100. No increased PRL or any of the other variants assayed were found in men. Results were similar when PRL was evaluated in the same blood samples by a different IRMA (DPC Laboratory). The etiology of the hyperprolactinemia in some of these patients is unknown, but their lack of symptoms (galactorrhea or amenorrhea) could be due to the BIG/BIG forms and basically to the glycosylation of the hormone. As for the relation between PRL and SLE activity, we found that hyperprolactinemic patients were younger, had a shorter history of illness, although it was not statistically significant, and a higher SLEDAI score. This would indicate a relation between hyperprolactinemia and lupus activity. The patients with increased BIG/BIG form also had a very active illness at the time of the study.

Prolactin and macroprolactin levels in psychiatric patients receiving atypical antipsychotics: A preliminary study

The aims of this study were to clarify whether atypical antipsychotics can elevate serum levels of both macroprolactin and prolactin, and whether the macroprolactin levels differ according to the type of atypical antipsychotic being taken. In total, 245 subjects were enrolled consecutively in 6 hospitals. Serum prolactin and macroprolactin levels were measured at a single time point during maintenance antipsychotic monotherapy. The mean total serum prolactin levels including macroprolactin were 11.91, 20.73, 16.41, 50.83, 12.84, and 59.1ng/mL for patients taking aripiprazole, blonanserin, olanzapine, paliperidone, quetiapine, and risperidone, respectively, while those for macroprolactin were 1.71, 3.86, 3.73, 7.28, 2.77, and 8.0ng/mL. The total prolactin and macroprolactin levels were significantly higher among those taking paliperidone and risperidone than among those taking any of the other antipsychotics (p<0.01). Moreover, there was a strong positive correlation between serum levels of prolactin and macroprolactin. Sexual dysfunction was reported in 35.5% (87/245) of the total subjects. However, the total prolactin level did not differ significantly between subjects with and without sexual dysfunction except gynecomastia. These findings suggest that treatment with risperidone and paliperidone can induce hyperprolactinemia and macroprolactinemia in psychiatric patients.

Prolactin levels correlate with abnormal B cell maturation in MRL and MRL/lpr mouse models of systemic lupus erythematosus-like disease

Prolactin (PRL) plays an important role in modulating the immune response. In B cells, PRL enhances antibody production, including antibodies with self-specificity. In this study, our aims were to determine the level of PRL receptor expression during bone-marrow B-cell development and to assess whether the presence of high PRL serum concentrations influences absolute numbers of developing populations and disease outcome in lupus-prone murine models. We observed that the PRL-receptor is expressed in early bone-marrow B-cell; the expression in lupus-prone mice, which had the highest level of expression in pro-B cells and immature cells, differed from that in wild-type mice. These expression levels did not significantly change in response to hyperprolactinemia; however, populations of pro-B and immature cells from lupus-prone strains showed a decrease in the absolute numbers of cells with high PRL-receptor expression in response to PRL. Because immature self-reactive B cells are constantly being eliminated, we assessed the expression of survival factor BIRC5, which is more highly expressed in both pro-B and immature B-cells in response to PRL and correlates with the onset of disease. These results identify an important role of PRL in the early stages of the B-cell maturation process: PRL may promote the survival of self-reactive clones.

Increased levels of prolactin receptor expression correlate with the early onset of lupus symptoms and increased numbers of transitional-1 B cells after prolactin treatment

Background

Prolactin is secreted from the pituitary gland and other organs, as well as by cells such as lymphocytes. Prolactin has an immunostimulatory effect and is associated with autoimmune diseases that are characterised by abnormal B cell activation, such as systemic lupus erythematosus (SLE). Our aim was to determine if different splenic B cell subsets express the prolactin receptor and if the presence of prolactin influences these B cell subsets and correlates with development of lupus.

Results

Using real-time PCR and flow cytometry, we found that different subsets of immature (transitional) and mature (follicular, marginal zone) B cells express different levels of the prolactin receptor and are differentially affected by hyperprolactinaemia. We found that transitional B cells express the prolactin receptor at higher levels compared to mature B cells in C57BL/6 mice and the lupus-prone MRL/lpr and MRL mouse strains. Transitional-1 (T1) B cells showed a higher level of prolactin receptor expression in both MRL/lpr and MRL mice compared to C57BL/6 mice. Hyperprolactinaemia was induced using metoclopramide, which resulted in the development of early symptoms of SLE. We found that T1 B cells are the main targets of prolactin and that prolactin augments the absolute number of T1 B cells, which reflects the finding that this B cell subpopulation expresses the highest level of the prolactin receptor.

Conclusions

We found that all B cell subsets express the prolactin receptor but that transitional B cells showed the highest prolactin receptor expression levels. Hyperprolactinaemia in mice susceptible to lupus accelerated the disease and increased the absolute numbers of T1 and T3 B cells but not of mature B cells, suggesting a primary effect of prolactin on the early stages of B cell maturation in the spleen and a role of prolactin in B cell differentiation, contributing to SLE onset.

Development of anti-PRL (prolactin) autoantibodies by homologous PRL in rats: a model for macroprolactinemia

Macroprolactinemia is hyperprolactinemia in humans mainly due to anti-PRL (prolactin) autoantibodies and is a pitfall for the differential diagnosis of hyperprolactinemia. Despite its high prevalence, the pathogenesis remains unclear. In this study, we examined whether anti-PRL autoantibodies develop via immunization with homologous rat pituitary PRL in rats to elucidate what mechanisms are involved and whether they cause hyperprolactinemia with low PRL bioactivity, as seen in human macroprolactinemia. Anti-PRL antibodies were developed in 19 of 20 rats immunized with homologous rat pituitary PRL and 29 of 30 rats with heterogeneous bovine or porcine pituitary PRL but did not develop in 25 control rats. In rats with anti-PRL antibodies, the basal serum PRL levels were elevated, and a provocative test for PRL secretion using dopamine D2 receptor antagonist (metoclopramide) showed a normal rising response with a slower clearance of PRL because of the accumulation of macroprolactin in blood. Antibodies developed by porcine or rat pituitary PRL reduced the bioactivity of rat serum PRL, and gonadal functions in these rats were normal despite hyperprolactinemia. Anti-PRL antibodies were stable and persisted for at least 5 wk after the final injection of PRL. These findings suggest that pituitary PRL, even if homologous, has antigenicity, leading to the development of anti-PRL autoantibodies. We successfully produced an animal model of human macroprolactinemia, with which we can explain the mechanisms of its clinical characteristics, i.e. asymptomatic hyperprolactinemia.

Correlation between serum prolactin levels and lupus activity

To assess the frequency of hyperprolactinemia and evaluate its possible clinical significance in patients with systemic lupus erythematosus (SLE). We determined serum prolactin (PRL) levels in 30 patients with SLE by a radioimmunometric assay. For each patient, the clinical disease activity was assessed using the Systemic Lupus Activity Measure. Antinuclear antibodies were determined by standard techniques. Correlation between PRL concentrations and SLE clinical and serological activity were evaluated. Elevated serum concentrations of PRL (>25 ng/ml in female and >16 ng/ml in male) were found in 10 of the 30 (33.3%) patients (7-85 ng/ml, mean 33.8, SD 19.8). A significant correlation was found between the PRL levels and the clinical disease activity of SLE (P < 0.001, r = 0.675). In addition, hyperprolactinemia was associated with serological activity. Hyperprolactinemia was frequently detected in patients with SLE. There is a significant correlation between hyperprolactinemia and lupus activity.

Macroprolactinemia: clinical significance and characterization of the condition

The purpose of this study was to characterize the clinical picture of macroprolactinemic patients and to further assess whether macroprolactinemia was part of an auto-immune syndrome. Eighty-two hyperprolactinemic (serum PRL > 1000 mU/l) patients were investigated and the PEG precipitation test identified 14 patients with macroprolactinemia (bb PRL). They were submitted to a hormonal and autoimmune screening and an IV TRH test. Bioactivity of their serum prolactin was evaluated, using an Nb2 assay. The biochemical nature of bb-PRL was investigated by immunoprecipitation with anti-IgG antibodies. Seventy-nine percent of the studied patients presented with infertility, amenorrhoea, galactorrhoea, mastodynia, gynaecomastia or erectile dysfunction. In most cases, however, these symptoms could be explained by the presence of other non hyperprolactinemia-related pathology. Despite the finding of in vitro biological activity in all macroprolactinemic sera tested, our results suggest a variable in vivo bioactivity of bb-PRL, probably related to a reduced capacity to cross vascular endothelium. In this study, we demonstrated that in 12 out of 13 samples (85%), bb-PRL consisted of PRL-IgG complexes. There was no clinical or laboratory evidence of auto-immunity.

Immunoglobulin G subclasses and prolactin (PRL) isoforms in macroprolactinemia due to anti-PRL autoantibodies

Although macroprolactinemia due to antiprolactin (anti-PRL) autoantibodies is not uncommon among hyperprolactinemic patients, the pathogenesis of such macroprolactinemia is still unknown. We examined IgG subclasses of anti-PRL autoantibodies by enzyme immunoassay, and PRL phosphorylation and isoforms by Western blotting, mass spectrometry, and two-dimensional electrophoresis in six patients with anti-PRL autoantibodies and in 29 controls. PRL-specific IgG subclasses in patients with anti-PRL autoantibodies were heterogeneous, but five of six patients showed IgG4 predominance, which is known to be produced by chronic antigen stimulation. Western blot and mass spectrometric analyses revealed that human pituitary PRL was phosphorylated at serine 194 and serine 163, whereas serine 163 in serum PRL was dephosphorylated. On two-dimensional electrophoresis, serum PRL mainly consisted of isoform with isoelectric point (pI) 6.58 in control hyperprolactinemic patients, whereas acidic isoforms (pIs 6.43 and 6.29) were also observed in patients with anti-PRL autoantibodies. Our data first demonstrate that human pituitary PRL is serine phosphorylated and partially dephosphorylated in serum, and suggest that the acidic isoforms may give rise to chronic antigen stimulation in patients with anti-PRL autoantibodies.

Neuroendocrine dopaminergic regulation of prolactin release in systemic lupus erythematosus: a possible role of lymphocyte-derived prolactin

Prolactin (PRL) secretion by the pituitary is under the control of dopamine. Hyperprolactinemia has been found in patients with systemic lupus erythematosus (SLE) and seems to be associated with clinical activity. T-lymphocytes express PRL and those from SLE patients appear to secrete more PRL than controls. In this study, immuno-(RIA) and bio-(BIO) assayable PRL in both serum and culture media of peripheral blood mononuclear cells (PBMNC) from SLE and control subjects were evaluated in the basal state and in response to 10 mg oral administration of metoclopramide, a dopamine receptor antagonist. Prolactin size heterogeneity in serum and culture media and PRL gene transcription in PBMNC were also studied. Basal serum RIA-PRL, BIO-PRL and the BIO/RIA ratio were similar in both groups. The serum BIO-PRL response after metoclopramide was higher than RIA-PRL in SLE, and this increment was also greater than in control subjects. PBMNC from SLE subjects secreted and produced more BIO-PRL. After metoclopramide, secretion and production of PRL increased only in PBMNC from control women and not in those from SLE patients. Our results demonstrated an increased central dopaminergic tone in SLE and suggest that lymphocyte-derived PRL might contribute to alter the functional activity of the hypothalamic dopaminergic system in SLE attempting to maintain serum PRL within a physiological range.

Macroprolactinemia: the consequences of a laboratory pitfall

The objective of this study was to assess the prevalence of macroprolactin, a macromolecule with reduced bioactivity, in hyperprolactinemic patients. Prolactin was measured before and after precipitation of macroprolactin by polyethylene glycol in 306 patients. Only patients with prolactin values >700 mIU/L (n = 270) entered the study. In 23% of the patients, macroprolactinemia was found. In women, the occurrence of macroprolactinemia increased with advancing age (< 30 yr: 16%; 30-45 yr: 28%; > 45 yr: 42%; p < 0.05). A priori clinical signs of hyperprolactinemia (morphological abnormalities in pituitary imaging, galactorrhea infertility) occurred significantly less frequently in macroprolactinemia than in true hyperprolactinemia. In eight females macroprolactinemia and true hyperprolactinemia appeared simultaneously. To avoid diagnostic and therapeutic pitfalls, the screening for macroprolactinemia of all patients with prolactin levels of > 700 mIU/ L is recommended.

Macroprolactinemia: predictability on clinical basis and detection by PEG precipitation with two different immunometric methods

Prolactin (PRL) in human serum is present in three species: monomeric PRL (23 kDA), big PRL (50-60 kDa) and big, big PRL (bb-PRL or macroprolactinemia) of 150-170 kDa. Macroprolactin seems to be mainly composed of a molecule of monomeric PRL and an immunoglobulin G anti PRL. Its biological activity is considered low or absent, but it is measured, at various degrees, by the immunoassay method, thus causing diagnostic problems. Polyethylene Glycol (PEG) has been employed to precipitate macroprolactin, allowing its detection. This method is not applicable to all immunoassays for technical reasons. Our aim was to evaluate: 1) the predictability of macroprolactin on a clinical basis; 2) the possibility of applying PEG precipitation to Abbott AxSYM analyzer beside Roche Elecsys (already approved). We classified 34 hyperprolactinemic women, on a clinical and imaging basis, in four groups: A: functional hyperprolactinemia; B: pituitary lesions hyperprolactinemia; C: probably macroprolactinemia; D: unclassifiable hyperprolactinemia and a "control" group E of 19 healthy women. PRL was assayed, both with Elecsys and AxSYM, before and after PEG serum treatment. Eleven out of twelve group C, and 5/7 group D patients showed macroprolactinemia, against 1/7 in A and 1/8 in B. PEG was suitable for AxSYM only after the same treatment of the calibration standards, thus performing outcomes overlapping Elecsys. For clinical purposes, in the presence of macroprolactinemia, besides the recovery ratio, molar or ponderal monomeric PRL assay should be calculated.

Stimulation of interferon regulatory factor-1 by prolactin

Prolactin (PRL), a pituitary peptide hormone, is known to regulate diverse cellular functions including proliferation, differentiation, angiogenesis and protection against apoptosis and inflammation. To understand the mechanism of PRL signaling in T cells, we have cloned both PRL and its receptor (PRL-R), one potent mediator of PRL signaling, Stat5b, and a panel of PRL-inducible immediate early genes from T cells. We are employing these genes as tools with which to understand how PRL regulates the expression of one target gene, the transcription factor interferon regulatory factor-1 (IRF-1), which is a multifunctional immune regulator gene. In investigating regulatory events along the PRL-R/JAK/Stat/IRF-1 signaling pathway, we show that Stat factors can activate as well as inhibit IRF-1 promoter activity and that cross-talk between Stat and NFkappaB signaling pathways also regulates IRF-1 promoter activity. These findings have much broader implications not only for T lymphocytes but also for other PRL responsive target cells and tissues.