Prolactin modulates the naive B cell repertoire

Hormones and B-cell development in health and autoimmunity

The development of B cells into antibody-secreting plasma cells is central to the adaptive immune system as they induce protective and specific antibody responses against invading pathogens. Various studies have shown that, during this process, hormones can play important roles in the lymphopoiesis, activation, proliferation, and differentiation of B cells, and depending on the signal given by the receptor of each hormone, they can have a positive or negative effect. In autoimmune diseases, hormonal deregulation has been reported to be related to the survival, activation and/or differentiation of autoreactive clones of B cells, thus promoting the development of autoimmunity. Clinical manifestations of autoimmune diseases have been associated with estrogens, prolactin (PRL), and growth hormone (GH) levels. However, androgens, such as testosterone and progesterone (P4), could have a protective effect. The objective of this review is to highlight the links between different hormones and the immune response mediated by B cells in the etiopathogenesis of systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and multiple sclerosis (MS). The data collected provide insights into the role of hormones in the cellular, molecular and/or epigenetic mechanisms that modulate the B-cell response in health and disease.

A quinazoline derivative suppresses B cell hyper-activation and ameliorates the severity of systemic lupus erythematosus in mice

Background: Aberrant autoreactive B cell responses contribute to the pathogenesis of systemic lupus erythematosus (SLE). Currently, there is no safe and effective drug for intervention of SLE. Quinazoline derivative (N4-(4-phenoxyphenethyl)quinazoline-4,6-diamine, QNZ) is a NF-κB inhibitor and has potent anti-inflammatory activity. However, it is unclear whether QNZ treatment can modulate B cell activation and SLE severity. Methods: Splenic CD19⁺ B cells were treated with QNZ (2, 10, or 50 nM) or paeoniflorin (200 μM, a positive control), and their activation and antigen presentation function-related molecule expression were examined by flow cytometry. MRL/lpr lupus-prone mice were randomized and treated intraperitoneally with vehicle alone, 0.2 mg/kg/d QNZ or 1 mg/kg/d FK-506 (tacrolimus, a positive control) for 8 weeks. Their body weights and clinical symptoms were measured and the frequency of different subsets of splenic and lymph node activated B cells were quantified by flow cytometry. The degrees of kidney inflammation and glycogen deposition were examined by hematoxylin and eosin (H&E) and PAS staining. The levels of serum autoantibodies and renal IgG, complement C3 deposition were examined by ELISA and immunofluorescence. Results: QNZ treatment significantly inhibited the activation and antigen presentation-related molecule expression of B cells in vitro. Similarly, treatment with QNZ significantly mitigated the SLE activity by reducing the frequency of activated B cells and plasma cells in MRL/lpr mice. Conclusion: QNZ treatment ameliorated the severity of SLE in MRL/lpr mice, which may be associated with inhibiting B cell activation, and plasma cell formation. QNZ may be an excellent candidate for the treatment of SLE and other autoimmune diseases.

Interferon Genes Are Influenced by 17β-Estradiol in SLE

Recent evidence suggests the existence of a nexus between inflammatory pathways and the female sex hormone 17β-estradiol, resulting in increased interferon-stimulated genes (ISGs), autoantibodies, and dysregulation of immune cells in SLE. However, the molecular mechanisms and the effect of estradiol on candidate target genes and their pathways remains poorly understood. Our previous work suggests that female SLE patients have increased estradiol levels compared to healthy controls. In the present study, we explored the effects of 17β-estradiol treatment on expression of IFN (interferons)-stimulated genes and pro-inflammatory cytokines/chemokines. We found significantly increased (5-10-fold) expression of IFN-regulated genes in healthy females. Furthermore, we found significantly increased plasma levels of IL-6, IL-12, IL-17, IL-18, stem cell factor (SCF), and IL-21/IL-23 in SLE patients compared to healthy controls, and those levels positively correlated with the plasma levels of 17β-estradiol. In addition, levels of IL-21 positively correlated with the SLE disease activity index (SLEDAI) score of SLE patients. In vitro treatment of PBMCs from either SLE patients or healthy controls with 17β-estradiol at physiological concentration (~50 pg/ml) also significantly increased secretion of many pro-inflammatory cytokines and chemokines (IL-6, IL-12, IL-17, IL-8, IFN-γ; MIP1α, and MIP1β) in both groups. Further our data revealed that 17β-estradiol significantly increased the percentage of CD3⁺CD69⁺ and CD3⁺IFNγ⁺ T cells; whereas, simultaneous addition of 17β-estradiol and an ERα inhibitor prevented this effect. Collectively, our findings indicate that 17β-estradiol participates in the induction of pro-inflammatory cytokines and chemokines and further influences interferon genes and pathways.

The expansion of activated naive DNA autoreactive B cells and its association with disease activity in systemic lupus erythematosus patients

BACKGROUND

Autoreactive B cells are well recognized as key participants in the pathogenesis of systemic lupus erythematosus (SLE). However, elucidating the particular subset of B cells in producing anti-dsDNA antibodies is limited due to their B cell heterogeneity. This study aimed to identify peripheral B cell subpopulations that display autoreactivity to DNA and contribute to lupus pathogenesis.

METHODS

Flow cytometry was used to detect total B cell subsets (n = 20) and DNA autoreactive B cells (n = 15) in SLE patients' peripheral blood. Clinical disease activities were assessed in SLE patients using modified SLEDAI-2 K and used for correlation analyses with expanded B cell subsets and DNA autoreactive B cells.

RESULTS

The increases of circulating double negative 2 (DN2) and activated naïve (aNAV) B cells were significantly observed in SLE patients. Expanded B cell subsets and DNA autoreactive B cells represented a high proportion of aNAV B cells with overexpression of CD69 and CD86. The frequencies of aNAV B cells in total B cell populations were significantly correlated with modified SLEDAI-2 K scores. Further analysis showed that expansion of aNAV DNA autoreactive B cells was more related to disease activity and serum anti-dsDNA antibody levels than to total aNAV B cells.

CONCLUSION

Our study demonstrated an expansion of aNAV B cells in SLE patients. The association between the frequency of aNAV B cells and disease activity patients suggested that these expanded B cells may play a role in SLE pathogenesis.

Sex Hormones and Gender Influence the Expression of Markers of Regulatory T Cells in SLE Patients

Regulatory T cells have been implicated in the regulation and maintenance of immune homeostasis. Whether gender and sex hormones differentially influence the expression and function of regulatory T cell phenotype and their influence on FoxP3 expression remains obscure. We provide evidence in this study that the number and percent of human regulatory T cells (T_regs) expressing CD4⁺ and CD8⁺ are significantly reduced in healthy females compared to healthy males. In addition, both CD4⁺CD25^+hi and CD8⁺CD25^+hi subsets in healthy males have a 2-3 fold increase in FoxP3 mRNA expression compared to healthy females. Female SLE patients, compared to healthy women, have elevated plasma levels of estradiol and decreased levels of testosterone. Higher levels of testosterone correlate with higher expression of FoxP3 in CD4⁺CD25^hiCD127^low putative T_regs in women with SLE. Incubation of CD4⁺ regulatory T cells with 17β-estradiol at physiological levels generally decreased FoxP3 expression in females with SLE. These data suggest that females may be more susceptible than males to SLE and other autoimmune diseases in part because they have fewer T_regs and reduced FoxP3 expression within those cells due to normal E2 levels which suppress FoxP3 expression. In addition, low levels of plasma testosterone in women may further reduce the ability of the T_regs to express FoxP3. These data suggest that gender and sex hormones can influence susceptibility to SLE via effects on regulatory T cells and FoxP3 expression.

Contributions of Major Cell Populations to Sjögren's Syndrome

Sjögren’s syndrome (SS) is a female dominated autoimmune disease characterized by lymphocytic infiltration into salivary and lacrimal glands and subsequent exocrine glandular dysfunction. SS also may exhibit a broad array of extraglandular manifestations including an elevated incidence of non-Hodgkin’s B cell lymphoma. The etiology of SS remains poorly understood, yet progress has been made in identifying progressive stages of disease using preclinical mouse models. The roles played by immune cell subtypes within these stages of disease are becoming increasingly well understood, though significant gaps in knowledge still remain. There is evidence for distinct involvement from both innate and adaptive immune cells, where cells of the innate immune system establish a proinflammatory environment characterized by a type I interferon (IFN) signature that facilitates propagation of the disease by further activating T and B cell subsets to generate autoantibodies and participate in glandular destruction. This review will discuss the evidence for participation in disease pathogenesis by various classes of immune cells and glandular epithelial cells based upon data from both preclinical mouse models and human patients. Further examination of the contributions of glandular and immune cell subtypes to SS will be necessary to identify additional therapeutic targets that may lead to better management of the disease.

Association Between BDNF Gene Variant Rs6265 and the Severity of Depression in Antidepressant Treatment-Free Depressed Patients

BACKGROUND

Brain-derived neurotrophic factor (BDNF) plays an important role in neuronal plasticity, and its dysregulation has been associated with the pathogenesis of mood and anxiety disorders. Prolactin (PRL) is a pituitary hormone which is also produced as a cytokine by immune cells and could be a neurotrophic factor regulating the functional activity of stress-related mechanisms.

AIM

To investigate the possible relationship between depressive state and BDNF and PRL genotypes or levels with special reference to severity of depression.

METHODS

Participants of 18-70 years with a clinical diagnosis of depressive disorder of at least moderate severity were included. These patients had not been treated with antidepressant drugs before admission to hospital during the preceding period of the last 6 months, and 54.5% had never been treated with antidepressant drugs during their entire life. The DNA was genotyped for rs1341239 within the prolactin and for rs6265, rs7124442, and rs11030104 within the BDNF gene. Rs11030104 violated the Hardy-Weinberg equilibrium distribution and was excluded from further analyses. BDNF and prolactin concentration was measured in serum by MAGPIX multiplex analyzer (Luminex, USA) using MILLIPLEX^® MAP kit (Merck, Germany). Genetic associations were determined by sequentially regressing prolactin, BDNF, 17-items Hamilton's Depression (HAMD-17) and Clinical Global Impression scale, Severity (CGI-S) ratings, and depression (absent/present) on the available SNPs. Genetic associations were evaluated assuming an additive model.

RESULTS

A total of 186 depressed patients (of which 169 were women) and 94 healthy controls (67 women) were genotyped. After excluding subjects without genetic information on all three study SNPs, 217 remained of whom 138 suffered from depression. Within depressed patients we observed an association of rs6265 with HAMD-17: mean difference (MD) 2.33 (95%CI 0.49; 4.16; p = 0.014) and CGI-S: MD 0.38 (95%CI 0.09; 0.66; p = 0.011). No significant association was observed between the prolactin SNP rs1341239 and prolactin levels. Similarly the mean differences of BDNF SNPs did not show an association with BDNF: rs6265 -0.042 ln(pg/ml) (95%CI -0.198; 0.113), and rs7124442 0.006 ln(pg/ml) (95%CI -0.117; 0.130). No other association reached statistical significance.

CONCLUSION

We observed a significant association between BDNF gene variant rs6265 and the severity of depression in newly admitted, antidepressant treatment-free, depressed patients. Actual PRL and BDNF levels were not elevated sufficiently in depressed patients to reach statistical significance and were not associated with the studied genotypes.

Autoimmune hypothyroidism is three times more frequent in female prolactinoma patients compared to healthy women: data from a cross-sectional case-control study

BACKGROUND

The potent immunomodulatory action of prolactin has been demonstrated in many experimental in vitro studies. In accordance with these data, our retrospective analyses revealed higher prevalence of autoimmune thyroid diseases in prolactinoma patients compared to general population.

PURPOSE

A cross-sectional case-control study was carried out in a single tertiary referral centre. The main aim was to assess the frequency of newly diagnosed autoimmune thyroid diseases in female patients with prolactinomas.

METHODS

The study population consisted of 260 females (154 patients and 106 sex-matched, ethnicity-matched, and age-matched healthy controls) enroled in a prospective manner. Physical exam, thyroid ultrasound, and laboratory testing (measurement of antibodies to thyroglobulin, thyroid peroxidase, TSH-receptor, serum TSH and FT4 levels) were performed in all study participants.

RESULTS

Autoimmune thyroid diseases were diagnosed in 29.9% of the patients and 10.4% of the healthy subjects (p  = 0.0002). Subclinical hypothyroidism was found in 9.7% of the patients versus 2.8% of the controls (p  = 0.044). Autoimmune hyperthyroidism was observed in 1.3% of all patients.

CONCLUSIONS

The prevalence of newly diagnosed autoimmune thyroid diseases, and especially the subclinical hypothyroidism, was significantly higher in our female prolactinoma patients in comparison to age-matched healthy women. Based on our results, we suggest routine screening for autoimmune thyroid diseases (thyroid function, immunology and ultrasound examination) in all female patients with prolactinoma at the time of diagnosis. We also recommend a close follow-up of thyroid function in these women in case of pregnancy and after delivery.

Prolactin: Friend or Foe in Central Nervous System Autoimmune Inflammation?

The higher prevalence of multiple sclerosis (MS) in females, along with the modulation of disease activity observed during pregnancy and the post-partum period, has suggested a hormonal influence in MS. Even if prolactin (PRL) does not belong to the sex hormones family, its crucial role in female reproduction and lactation has prompted great efforts to understand if PRL could represent a gender factor in the pathogenesis of MS and experimental autoimmune encephalomyelitis (EAE), the animal model for this disease. Extensive literature has documented a remarkable immune-stimulating potential for this hormone, indicating PRL as a disease-promoting factor in MS and EAE. However, recent work has pointed out that PRL is endowed with important neuroprotective and remyelinating properties and has encouraged a reinterpretation of the involvement of this hormone in MS. In this review we summarize both the protective functions that PRL exerts in central nervous system tissue as well as the inflammatory activity of this hormone in the context of autoimmune responses against myelin. Last, we draw future lines of research that might help to better clarify the impact of PRL on MS pathology.

The prolactin receptor is expressed in rheumatoid arthritis and psoriatic arthritis synovial tissue and contributes to macrophage activation

Objectives. Prolactin (PRL) is a lactation-inducing hormone with immunomodulatory properties and is found at elevated levels in the serum of patients with RA and other rheumatic diseases. The PRL receptor (PRLR) has been shown to be expressed by macrophages in atherosclerotic plaques. The aim of this study was to examine PRLR expression by synovial macrophages and its role in the regulation of macrophage activation.

Methods. Serum monomeric 23 kDa PRL levels were measured in 119 RA patients using a fluoroimmunometric assay. PRLR expression was assessed in synovial tissue of 91 RA, 15 PsA and 8 OA patients by immunohistochemistry and digital image analysis. Double IF was used to identify PRLR-expressing cells. The effects of PRL on monocyte-derived macrophage gene expression were examined by quantitative real-time PCR and ELISA.

Results. Serum PRL levels were similar in female and male RA patients. Median (interquartile range) PRLR expression was significantly higher (P < 0.05) in RA and PsA synovial tissue compared with OA. PRLR colocalized with synovial CD68⁺ macrophages and von Willebrand factor⁺ endothelial cells. In vitro, PRLR was prominently expressed in IFN-γ-and IL-10-polarized macrophages compared with other polarizing conditions. PRL by itself had negligible effects on macrophage gene expression, but cooperated with CD40L and TNF to increase expression of pro-inflammatory genes including IL-6, IL-8 and IL-12β.

Conclusions. Synovial PRLR expression is enhanced in patients with inflammatory arthritis compared with OA, and PRL cooperates with other pro-inflammatory stimuli to activate macrophages. These results identify PRL and PRLR as potential new therapeutic targets in inflammatory arthritis.

Prolactin and Dehydroepiandrosterone Levels in Women with Systemic Lupus Erythematosus: The Role of the Extrapituitary Prolactin Promoter Polymorphism at -1149G/T

Systemic lupus erythematosus (SLE) has shown an association with high levels of prolactin, low levels of dehydroepiandrosterone (DHEA), and induction of inflammatory cytokines in the serum of patients with the disease. This preliminary study examined the relevance of a −1149G/T functional single-nucleotide polymorphism (SNP) (rs1341239) in the promoter of the extrapituitary prolactin gene in a cohort of African American and European American women with lupus. Examination of this SNP revealed that the −1149TT genotype was correlated with higher levels of prolactin in serum and prolactin gene expression (p = 0.0001) in peripheral blood mononuclear cells (PBMCs). Lower levels of DHEA in serum were demonstrated in lupus patients (p = 0.001); those with the −1149TT genotype had the lowest levels of DHEA. Furthermore, a small subset of women who were on DHEA therapy and had a TT genotype showed a significant decrease in prolactin gene expression and lower disease activity scores (SLEDAI). Lupus patients, particularly African Americans, had significantly higher levels of IL-6 (p = 0.0001) and TNF-α (p = 0.042). This study suggests that the −1149TT genotype may be a risk factor for lupus and may predict who could possibly benefit from DHEA therapy; therefore, these results should be validated in a larger cohort with all ethnic groups.

Pregnancy and the Immune System: General Overview and the Gastroenterological Perspective

Pregnancy represents a unique immune tolerant condition that cannot be attributed merely to generalized immunosuppression. A variety of mechanisms have been described, ranging from the non-self recognition, immunomodulation of specific inflammatory cell populations and a Th2-directed shift of the immune response, which are mediated by both localized and systemic mediators. Furthermore, an inflammatory response directed toward the conceptus is no longer considered an obligatory deleterious response; instead, it is considered an important factor that is necessary for normal growth and development. These immunomodulatory changes during pregnancy may also affect concurrent conditions and alter the course of inflammatory diseases. Herein, we review the main immunomodulatory changes that occur during pregnancy and their effect on coexisting inflammatory conditions, with a specific focus on gastrointestinal disorders.

Interferon regulatory factor 1 marks activated genes and can induce target gene expression in systemic lupus erythematosus

OBJECTIVE

Interferon regulatory factor 1 (IRF-1) mediates both induction of interferons (IFNs) and responses to type I IFNs. It has been implicated as a critical mediator of inflammation in murine lupus models. In a previous study of chromatin modifications in monocytes from patients with systemic lupus erythematosus (SLE), IRF-1 was implicated as being associated with increased histone acetylation in this disease. The present study was undertaken to directly investigate IRF-1 binding sites on chromatin.

METHODS

Cells from 9 female SLE patients and 7 female controls were examined. Monocytes were purified from peripheral blood and subjected to library preparation using a validated antibody to IRF-1. IRF-1 binding sites on chromatin were identified by chromatin immunoprecipitation followed by sequencing. The effect of IRF-1 on target gene expression was confirmed using an overexpression system in cell lines, and coimmunoprecipitation was used to identify protein interactions.

RESULTS

IRF-1 binding around transcribed regions was increased in SLE patient monocytes, but histone modifications at potential IRF-1 binding sites without detectable IRF-1 binding were increased as well. Overexpression of IRF-1 was sufficient to drive transcription of target genes. IRF-1 overexpression was also able to alter histone modifications at a focus set of target genes, and treatment with an IRF-1 inhibitor reduced both expression and histone modifications at target genes. IRF-1 was found to interact with a select set of histone-modifying enzymes and other transcription factors.

CONCLUSION

IRF-1 is an important signaling protein in the interferon pathway. It not only activates gene expression as a transcription factor, but may perpetuate disease by leading to a dysregulated epigenome.

Acute onset polymyositis after prolactinoma extirpation

Hyperprolactinemia has been related to autoimmune diseases. Herein, we describe a case of a female with a prolactin producer pituitary macroadenoma who developed severe polymyositis one month after its removal. The patient had very high levels of CPK and muscle biopsy showed remarkable inflammatory infiltration. Steroid therapy was followed with total recovery. To the best of our knowledge, this is the first case reported of acute polymyositis after pituitary macroadenoma exeresis.

Hormonal milieu at time of B cell activation controls duration of autoantibody response

A strong gender bias is seen in many autoimmune diseases including systemic lupus erythematosus (SLE). To investigate the basis for the female preponderance in SLE, we have been studying BALB/c mice in which B cells express the R4A heavy chain of an anti-DNA antibody in association with an endogenous light chain repertoire (R4Atg mice). In unmanipulated mice, approximately 5% of B cells express the R4A transgene. R4Atg mice do not spontaneously develop elevated serum titers of anti-DNA antibodies. Administration of either estradiol (E2) or prolactin (Pr) results in escape from tolerance of autoreactive B cells, expressed as an increase in transgene-expressing B cells and elevated serum titers of anti-DNA antibodies. We previously demonstrated that autoreactive B cells maturing in an estrogenic milieu develop as marginal zone (MZ) B cells; when these same B cells mature in the presence of increased prolactin, they develop as follicular (Fo) B cells. To determine the long term consequence of this differential maturation of DNA-reactive B cells, we treated R4Atg BALB/c mice with E2 or Pr for 6 weeks until serum titers of anti-DNA antibody were high, at which time hormonal exposure was discontinued. In E2-treated mice, the anti-DNA titers remained high even 3 months after discontinuation of hormone exposure. Nascent B cells underwent normal tolerance induction, but existing autoreactive MZ B cells persisted and continued to secrete autoantibody. In contrast, Pr caused only a short-term increase in anti-DNA antibody titers. By 3 months after cessation of hormone treatment, serum anti-DNA antibody titers and B cell subsets were indistinguishable from those in placebo (P) treated mice. These findings suggest that autoantibody responses are sustained for variable lengths of time depending on the B cell subset producing the autoantibodies. This observation may be relevant to understanding the heterogeneous presentation of patients with SLE and to the design of therapies targeting specific B-cell populations in autoimmune disease.

Prolactin rescues and primes autoreactive B cells directly and indirectly through dendritic cells in B6.Sle3 mice

The lupus susceptibility interval Sle3/5 confers responsiveness to prolactin in C57BL/6 (B6) mice and hyperprolactinaemia induces a lupus-like phenotype in B6.Sel3/5 mice. In this study, the immunostimulatory effects of prolactin in B6 mice containing the Sle3 portion of the Sel3/5 interval (B6.Sle3 mice) were dissected. Because of the Sle3 interval's involvement in activation of myeloid cells, the effect of dendritic cells (DCs) from prolactin-treated B6.Sle3 mice on the phenotype of B6 mice was also evaluated. B cells from prolactin-treated B6 and B6.Sle3 mice and from B6 recipients of prolactin-modulated DCs from B6.Sle3 mice were tested for DNA-reactivity and resistance to B cell receptor (BCR)-mediated apoptosis. The expression of co-stimulatory molecules on lymphocytes and myeloid cells was also evaluated. In prolactin-treated B6.Sle3 mice, transitional type 2 B cells increased while type 1 B cells decreased as a consequence of prolactin-induced resistance to BCR-mediated apoptosis leading to the survival of DNA-reactive B cells. Follicular B cells from prolactin-treated mice expressed increased levels of CD40, B7·2 and IA(b), and DCs and monocytes had higher levels of CD44 and B7·2 than placebo-treated mice. Adoptive transfer of DCs from prolactin-treated B6.Sle3 mice to B6 recipients demonstrated the intrinsic ability of prolactin-modulated DCs to induce a development of lupus-like characteristics in B6 mice. Based on these results, prolactin accelerates the breakdown of immune tolerance in B6.Sle3 mice by promoting the survival, maturation and activation of autoreactive B cells, DCs and macrophages.

Menstrual and reproductive factors, and hormonal contraception use: associations with non-Hodgkin lymphoma in a pooled analysis of InterLymph case-control studies

BACKGROUND

The two most common forms of non-Hodgkin lymphoma (NHL) exhibit different sex ratios: diffuse large B-cell lymphoma (DLBCL) occurs more frequently in men and follicular lymphoma (FL) more frequently in women. Looking among women alone, this pooled analysis explores the relationship between reproductive histories and these cancers.

MATERIALS AND METHODS

Self-reported reproductive histories from 4263 women with NHL and 5971 women without NHL were pooled across 18 case-control studies (1983-2005) from North America, Europe and Japan. Study-specific odd ratios (ORs) and confidence intervals (CIs) were estimated using logistic regression and pooled using random-effects meta-analyses.

RESULTS

Associations with reproductive factors were found for FL rather than NHL overall and DLBCL. In particular, the risk of FL decreased with increasing number of pregnancies (pooled OR(trend) = 0.88, 95% CI 0.81-0.96). FL was associated with hormonal contraception (pooled OR = 1.30, 95% CI 1.04-1.63), and risks were increased when use started after the age of 21, was used for <5 years or stopped for >20 years before diagnosis. DLBCL, on the other hand, was not associated with hormonal contraception (pooled OR = 0.87, 95% CI 0.65-1.16).

CONCLUSIONS

Hormonal contraception is associated with an increased risk of FL but not of DLBCL or NHL overall.

Autoreactive preplasma cells break tolerance in the absence of regulation by dendritic cells and macrophages

The ability to induce Ab responses to pathogens while maintaining the quiescence of autoreactive cells is an important aspect of immune tolerance. During activation of TLR4, dendritic cells (DCs) and macrophages (MFs) repress autoantibody production through their secretion of IL-6 and soluble CD40L (sCD40L). These soluble mediators selectively repress B cells chronically exposed to Ag, but not naive cells, suggesting a means to maintain tolerance during TLR4 stimulation, yet allow immunity. In this study, we identify TNF-α as a third repressive factor, which together with IL-6 and CD40L account for nearly all the repression conferred by DCs and MFs. Similar to IL-6 and sCD40L, TNF-α did not alter B cell proliferation or survival. Instead, it reduced the number of Ab-secreting cells. To address whether the soluble mediators secreted by DCs and MFs functioned in vivo, we generated mice lacking IL-6, CD40L, and TNF-α. Compared to wild-type mice, these mice showed prolonged anti-nuclear Ab responses following TLR4 stimulation. Furthermore, adoptive transfer of autoreactive B cells into chimeric IL-6(-/-) × CD40L(-/-) × TNF-α(-/-) mice showed that preplasma cells secreted autoantibodies independent of germinal center formation or extrafollicular foci. These data indicate that in the absence of genetic predisposition to autoimmunity, loss of endogenous IL-6, CD40L, and TNF-α promotes autoantibody secretion during TLR4 stimulation.

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.

The multi-faceted influences of estrogen on lymphocytes: toward novel immuno-interventions strategies for autoimmunity management

Early studies of the immune system disclosed that, generally, females exhibit stronger responses to a variety of antigens than males. Perhaps as a result of this response, women are more prone to developing autoimmune diseases than men. Yet, the precise cellular and molecular mechanisms remain under investigation. Recently, interferon-gamma and the related pro-inflammatory interleukin-12 were found to be under effects of sex steroid hormones, with potential implications in regulating immune cells and autoimmune responses. In B lymphocytes, functional binding sites for estrogen receptors were identified in the promoter of the gene encoding activation-induced deaminase, an enzyme required for somatic hypermutation, and class-switch recombination. The observation that estrogen exerts direct impacts on antibody affinity-maturation provides a potential mechanism that could account for generating pathogenic high-affinity auto-antibodies. Further deciphering the multi-faceted influences of sex hormones on the responsiveness of immune cells could lead to novel therapeutic interventions for autoimmunity management.

Prolactin, systemic lupus erythematosus, and autoreactive B cells: lessons learnt from murine models

The predominant prevalence of autoimmune diseases in women of reproductive age has led to the investigation of the effects of sex hormones on immune regulation and in autoimmune diseases, in particular the prototypic systemic autoimmune disease lupus. The female hormone prolactin has receptors beyond the reproductive axis including immune cells, and it is thought to promote autoimmunity in human and murine lupus. Induced hyperprolactinemia in experimental lupus models, regardless of gender, exacerbates disease activity and leads to premature death. Prolactin treatment in mice that are not prone to develop lupus leads to the development of a lupus-like phenotype. Persistent mild-moderate hyperprolactinemia alters the selection of the naïve B cell repertoire. Recent studies demonstrate that prolactin impairs all three mechanisms of B cell tolerance induction (negative selection, receptor editing, and anergy) and thereby contributes to the pathogenesis of autoimmunity. The effects of prolactin are genetically determined as shown by the differential response to the hormone in the different mice strains. Bromocriptine, a drug that inhibits prolactin secretion, abrogates some of the immune effects of this hormone. Further research is required to elucidate molecular mechanisms involved in immune effects of prolactin and to develop novel targeted treatments for SLE patients with prolactin-responsive disease.

Lessons from an anti-DNA autoantibody

R4A is an anti-DNA antibody derived by hybridoma technology from a BALB/c mouse. The study of its properties has helped to elucidate aspects of the physiopathology of Systemic Lupus Erythematosus (SLE). It has been useful to decipher the mechanisms implicated in breaks in B cell self tolerance by B cell extrinsic or B cell intrinsic factors. Furthermore, it illustrates the importance of molecular mimicry in understanding the cellular and molecular effects relevant to some manifestations of neuropsychiatric lupus, as it cross-reacts with the D/E W D/E YS/G peptide sequence present in subunits of the N-methyl d-aspartate receptor (NMDAR).

Phenotypic characterization of autoreactive B cells--checkpoints of B cell tolerance in patients with systemic lupus erythematosus

DNA-reactive B cells play a central role in systemic lupus erythematosus (SLE); DNA antibodies precede clinical disease and in established disease correlate with renal inflammation and contribute to dendritic cell activation and high levels of type 1 interferon. A number of central and peripheral B cell tolerance mechanisms designed to control the survival, differentiation and activation of autoreactive B cells are thought to be disturbed in patients with SLE. The characterization of DNA-reactive B cells has, however, been limited by their low frequency in peripheral blood. Using a tetrameric configuration of a peptide mimetope of DNA bound by pathogenic anti-DNA antibodies, we can identify B cells producing potentially pathogenic DNA-reactive antibodies. We, therefore, characterized the maturation and differentiation states of peptide, (ds) double stranded DNA cross-reactive B cells in the peripheral blood of lupus patients and correlated these with clinical disease activity. Flow cytometric analysis demonstrated a significantly higher frequency of tetramer-binding B cells in SLE patients compared to healthy controls. We demonstrated the existence of a novel tolerance checkpoint at the transition of antigen-naïve to antigen-experienced. We further demonstrate that patients with moderately active disease have more autoreactive B cells in both the antigen-naïve and antigen-experienced compartments consistent with greater impairment in B cell tolerance in both early and late checkpoints in these patients than in patients with quiescent disease. This methodology enables us to gain insight into the development and fate of DNA-reactive B cells in individual patients with SLE and paves the way ultimately to permit better and more customized therapies.

Prolactin alters the mechanisms of B cell tolerance induction

OBJECTIVE

Autoimmune diseases predominantly affect women, suggesting that female sex hormones may play a role in the pathogenesis of such diseases. We have previously shown that persistent mild-to-moderate elevations in serum prolactin levels induce a break in self tolerance in mice with a BALB/c genetic background. The aim of this study was to evaluate the effects of hyperprolactinemia on the mechanisms of B cell tolerance induction.

METHODS

Effects of prolactin on splenic B cell subsets were studied in female BALB/c mice. B cell receptor (BCR)-mediated apoptosis and proliferation of transitional B cells were analyzed by flow cytometry. Expression of apoptotic genes was examined by microarrays and real-time polymerase chain reaction analysis. B cells coexpressing kappa/lambda light chains were assessed by flow cytometry and immunohistochemistry. Activation status of transitional type 3 (T3) B cells was evaluated by BCR-induced calcium influx studies.

RESULTS

BCR-mediated apoptosis of the T1 B cell subset, a major checkpoint for negative selection of autoreactive specificities, was decreased in prolactin-treated mice. Microarray studies indicated that this event may be mediated by the prolactin-induced up-regulation of the antiapoptotic gene interferon-gamma receptor type II and down-regulation of the proapoptotic gene Trp63. Prolactin treatment also altered the amount of receptor editing, as indicated by the increased number of transitional B cells coexpressing kappa/lambda light chains. Additionally, hyperprolactinemia modified the level of B cell anergy by increasing the degree of BCR-induced calcium influx in the T3 B cells.

CONCLUSION

Persistently elevated serum prolactin levels interfere with B cell tolerance induction by impairing BCR-mediated clonal deletion, deregulating receptor editing, and decreasing the threshold for activation of anergic B cells, thereby promoting autoreactivity.

Selective regulation of autoreactive B cells by FcgammaRIIB

FcgammaRIIB is an inhibitory receptor which plays a role in limiting B cell and DC activation. Since FcgammaRIIB is known to dampen the signaling strength of the BCR, we wished to determine the impact of FcgammaRIIB on the regulation of BCRs which differ in their affinity for DNA. For these studies, FcgammaRIIB deficient BALB/c mice were bred with mice expressing the transgene-encoded H chain of the R4A anti-DNA antibody which gives rise to BCRs which express high, low or no affinity for DNA. The deletion of FcgammaRIIB in R4A BALB/c mice led to an alteration in the B cell repertoire, allowing for the expansion and activation of high affinity DNA-reactive B cells. By 6-8 months of age, R4A x FcgammaRIIB-/- BALB/c mice spontaneously developed anti-DNA antibody titers. These mice also displayed an induction of IFN-inducible genes and an elevation in levels of the B cell survival factor, BAFF. These data demonstrate that FcgammaRIIB preferentially limits activation of high affinity autoreactive B cells and can influence the activation of DC through an immune complex-mediated mechanism.

Diminished prolactin from chlordecone treatment in ovariectomized (NZBxNZW)F(1) mice

In murine models of systemic lupus erythematosus (SLE), administration of either prolactin or estradiol (E2) increases autoimmunity, and there is evidence that elevated prolactin in response to E2 administration may contribute substantially to E2 effects. Hormonal influence on SLE can extend to environmental agents, as demonstrated by the ability of estrogenic organochlorine pesticides such as chlordecone to accelerate the development of lupus in female (NZBxNZW)F(1) mice. In order to evaluate a potential role for prolactin in chlordecone effects on SLE, it was necessary to first determine whether treatment with chlordecone, like E2, results in elevated prolactin levels. Ovariectomized (NZBxNZW)F(1) mice were treated for 5-6 weeks with chlordecone or E2 in doses shown previously to significantly shorten the time to onset of SLE. At the end of the treatment period, serum prolactin levels were increased 10- to 20-fold in E2-treated mice compared to untreated controls, but decreased in an apparent dose-dependent manner in mice treated with chlordecone. Prolactin receptor in purified splenic B and CD4 T cells from treated animals, assessed through measurement of mRNA using quantitative real-time PCR, was increased by E2 treatment but unchanged in response to chlordecone. These observations suggest that the role of prolactin in eliciting autoimmunity in E2-treated animals is absent in the case of chlordecone, and by implication, that chlordecone possesses other actions that can replace the contribution of prolactin to development of SLE.

Control of the B cell-intrinsic tolerance programs by ubiquitin ligases Cbl and Cbl-b

B cell receptor (BCR) signaling plays a critical role in B cell tolerance and activation. Here, we show that mice with B cell-specific ablation of both Cbl and Cbl-b (Cbl-/-Cblb-/-) manifested systemic lupus erythematosus (SLE)-like autoimmune disease. The Cbl double deficiency resulted in a substantial increase in marginal zone (MZ) and B1 B cells. The mutant B cells were not hyperresponsive in terms of proliferation and antibody production upon BCR stimulation; however, B cell anergy to protein antigen appeared to be impaired. Concomitantly, BCR-proximal signaling, including tyrosine phosphorylation of Syk tyrosine kinase, Phospholipase C-gamma2 (PLC-gamma2), and Rho-family GTP-GDP exchange factor Vav, and Ca2+ mobilization were enhanced, whereas tyrosine phosphorylation of adaptor protein BLNK was substantially attenuated in the mutant B cells. These results suggested that the loss of coordination between these pathways was responsible for the impaired B cell tolerance induction. Thus, Cbl proteins control B cell-intrinsic checkpoint of immune tolerance, possibly through coordinating multiple BCR-proximal signaling pathways during anergy induction.

Human prolactin promotes human secondary immunoglobulin response in human/SCID mouse chimeras

Recombinant human prolactin (rhPRL) was administered to huPBL-SCID mice to determine its effects on production of human immunoglobulin (Ig). The huPBL-SCID mice were injected intraperitoneally (i.p.) with 10 mug rhPRL every other day for a total of 10 injections. The results reconfirmed that rhPRL significantly increased the numbers of human CD3+ T cells and human CD19+ B cells in spleens, lymph nodes, and thymuses of huPBL-SCID mice. The huPBL-SCID mice were then concurrently given various doses of diphtheria-tetanus (DT) vaccine and 10-mug i.p. injections of rhPRL and were examined for the presence of human DT-specific proliferation of lymph node cells in vitro and antibody production in vivo. rhPRL greatly improved the engraftment of functional human lymphocytes (CD3+ T cells and CD19+ B cells) in DT-immunized huPBL-SCID mice. The rhPRL-treated, DT-immunized huPBL-SCID mice produced significantly larger amounts of DT-specific antibodies in response to the vaccine. The predominant Ig isotype induced after immunization was IgG. Thus, rhPRL stimulation promotes human secondary IgG responses in huPBL-SCID mice.

Prolactinoma and systemic lupus erythematosus: do serum prolactin levels matter?

The lactogenic hormone prolactin is produced in part by cells of the immune system and serves as an upregulator of immune function. Hyperprolactinemia is common in patients with systemic lupus erythematosus (SLE), raising the possibility that the hormone contributes to the excessive immune response in the disease. The highest levels of circulating prolactin occur in association with prolactin-secreting tumors, but prolactinomas have only rarely been encountered in patients with SLE. We present here three patients with SLE and prolactinomas. As with the previously reported six patients, there was no consistency in the presence of findings related to prolactin excess or in the coincidence of hyperprolactinemia with flares of SLE disease activity. We speculate that this may be due to genetic differences in the response to prolactin and/or to the presence of variant prolactin isoforms detected in the clinical immunoassay that have reduced or absent biologic activity.

Balancing diversity and tolerance: lessons from patients with systemic lupus erythematosus

The autoimmune disease systemic lupus erythematosus (SLE) is caused by a failure of B cell tolerance. Recent studies in mouse models of SLE have identified several distinct tolerance checkpoints that must each function appropriately to protect against disease. However, studies of B cell repertoire selection in humans are essential to understand which checkpoints are defective in human autoimmune diseases.