Elena Peeva

Prolactin modulates the naive B cell repertoire

Prolactin is a peptide hormone produced by the anterior pituitary gland that is critical in lactation. Prolactin can also be produced by lymphocytes, and both B and T cells express prolactin receptors. These findings have suggested that prolactin has immunomodulatory functions. Studies in spontaneously autoimmune hosts have demonstrated a role for prolactin in augmenting autoreactivity. We chose to analyze prolactin effects on anti-DNA B cells in nonspontaneously autoimmune female BALB/c mice transgenic for the heavy chain of an anti-DNA antibody. Treatment with prolactin for 4 weeks induced a lupus-like phenotype with an increased number of transgene-expressing B cells, elevated serum anti-DNA antibody titers, and glomerular immunoglobulin deposits. Prolactin caused a decrease in the population of transitional B cells and an increase in mature follicular and marginal zone B cells. The DNA-reactive B cells had a follicular cell phenotype. Anti-DNA hybridomas demonstrated that prolactin alters selection of the naive B cell repertoire. The expansion and activation of anti-DNA B cells in prolactin-treated R4A-gamma2b BALB/c mice was dependent on the presence of CD4(+) T cells. Finally, treatment with prolactin was unable to break tolerance in R4A-gamma2b transgenic C57Bl/6 mice, suggesting that responsiveness of the immune system to prolactin is genetically determined.

Bromocriptine restores tolerance in estrogen-treated mice

Estrogen can modulate autoimmunity in certain models of systemic lupus erythematosus. Recently, we have shown that it can mediate survival and activation of anti-DNA B cells in a mouse transgenic for the heavy chain of a pathogenic anti-DNA antibody. To identify whether estrogen effects reflect increased prolactin secretion, we characterized B-cell autoreactivity in transgenic mice given both bromocriptine (an inhibitor of prolactin secretion) and estradiol. Treatment of mice with estradiol plus bromocriptine led to reduced titers of anti-DNA antibodies and diminished IgG deposition in kidneys compared with treatment with estradiol alone. However, mice treated with estradiol plus bromocriptine showed an expansion of transgene-expressing B cells and enhanced Bcl-2 expression, similar to those of estradiol-treated mice. We identified anergic high-affinity anti-DNA B cells in mice treated with estradiol plus bromocriptine, and we showed by molecular analysis of anti-DNA hybridomas that their B cells derive from a naive repertoire. Thus, the estradiol-induced breakdown in B-cell tolerance can be abrogated by bromocriptine, which induces anergy in the high-affinity DNA-reactive B cells. These studies demonstrate that some of the effects of estrogen on naive autoreactive B cells require the presence of prolactin and, thus, suggest potential therapeutic interventions in lupus.

Cutting Edge: Hormonal Milieu, Not Antigenic Specificity, Determines the Mature Phenotype of Autoreactive B Cells

Although both marginal zone and follicular B cells produce anti-DNA Abs in murine models of systemic lupus erythematosus, it has been unclear whether these distinct B cell subsets make identical or different Abs. Single-cell analysis demonstrates that the same DNA-reactive B cells can mature to either subset, depending on the hormonal environment. Anti-DNA B cells in estradiol-treated mice become marginal zone cells while identical cells from prolactin-treated mice become follicular cells. The B cell receptor signaling pathway is influenced by hormonal milieu. Thus, hormonal milieu and perhaps B cell receptor signaling, but not antigenic specificity, correlates with the differentiation pathway. These observations have implications for the pathogenesis and treatment of autoimmune disease.

Tamoxifen Blocks Estrogen-Induced B Cell Maturation but Not Survival

Estrogen treatment has been shown not only to exacerbate disease activity and accelerate death in spontaneous murine models of lupus but also to induce a lupus-like phenotype in nonspontaneously autoimmune mice. In mice transgenic for the H chain of an anti-DNA Ab, estrogen rescues naive autoreactive B cells that normally are deleted and causes them to mature to a marginal zone phenotype. Estrogen further leads to the activation of this population causing an elevation of serum anti-DNA Ab titers and renal disease. This study was designed to evaluate the therapeutic potential of tamoxifen, a selective estrogen receptor modulator, on estrogen-induced lupus. Mice treated with both estradiol and tamoxifen showed no elevation in anti-DNA Ab titers and consequently no glomerular IgG. The DNA-reactive B cell population that is rescued by estrogen was present in an anergic state in mice treated with both estradiol and tamoxifen. Estradiol enhances transitional B cell resistance to apoptosis and expands the population of marginal zone B cells; tamoxifen did not impede the enhanced resistance to apoptosis, but prevented the development of autoreactive cells as marginal zone B cells. Thus, estrogen-induced autoimmunity proceeds through two distinct molecular pathways, one affecting survival and the other maturation. Activation, but not survival, of autoreactive B cells can be abrogated by tamoxifen. Drugs that modulate even some of the effects of estrogen may be beneficial in patients with lupus. Eventually, understanding the pathways involved in survival and activation of autoreactive B cells will permit the development of therapeutics that target all relevant pathways.

B-cell directed therapies in antiphospholipid antibody syndrome — New directions based on murine and human data

The increased awareness of the role of humoral immunophysiology in antiphospholipid syndrome (APS) has aroused interest in B cells as therapeutic targets in this disease. This paper reviews the literature on B cell directed therapies in human and experimental APS. The clinical data is limited to B cell depletion with rituximab and comprises case reports and case series. Murine studies include use of modulators of B cell function such as belimumab and abatacept. In both human and murine studies, B cell directed therapies appeared to have clinical and serologic beneficial effects including a decrease in the antiphospholipid antibody titers after treatment. Randomized controlled clinical trials are needed to determine whether B cell depletors and/or B cell modulators can be effective agents for treating patients with APS.

B-Cell-Directed Therapies in Systemic Lupus Erythematosus

OBJECTIVE Owing to their ability to promote the onset and flares of systemic lupus erythematosus (SLE), B-cells are now established as key players in the pathogenesis of the disease, and, therefore, have become a major therapeutic focus in SLE. In this article, we review the literature on B-cell-directed therapies for SLE focusing on B-cell depletion, B-cell tolerance, costimulatory signals, and cytokines that affect B-cell survival and activation. METHODS The clinical trials reviewed in this article were accessed from the PubMed database (www.pubmed.gov) and Clinical Trials database (www.clinicaltrials.gov) through an English language search of the literature published between January 2002 and March 2007. Keywords included the following terms: B-cells, SLE, and therapy. RESULTS Seventeen completed clinical trials enrolling 973 patients and 5 ongoing studies with anticipated enrollment of 785 patients were reviewed. Novel SLE therapies that target B-cells directly or indirectly were included. B-cell-depleting therapies with the monoclonal antibodies rituximab and epratuzumab have shown good therapeutic results. On the contrary, the well-studied B-cell tolerogen LJP 394 has not demonstrated much clinical benefit. Studies targeting costimulatory pathways have shown variable results; clinical trials with anti-CD40L antibody were terminated because of thromboembolic events, whereas studies targeting the B7-CD28 pathway seem promising. Anticytokine agents against B-lymphocyte stimulator (BLyS), interleukin (IL)-10, IL-6, and interferon alpha (IFN-alpha) are the newcomers that need further evaluation in the treatment of SLE. CONCLUSIONS Progress in technology has led to the variety of B-cell-directed therapies. In contrast to general immunosuppressants, novel treatments that interfere with specific aspects of B-cell functions create the possibility of developing targeted therapeutic approaches for specific subpopulations of lupus patients.

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.

B-cell biology.

In recent years, our understanding of B-cell biology and the roles of B cells in normal immune responses and autoimmunity has increased dramatically. We no longer think of B cells simply as antibody factories. It is clear that these diverse and exquisitely regulated cells may contribute in a multitude of ways to immune responses. Animal models, clinical trials of biologic agents, and the ever expanding field of molecular biology have made great contributions to our current knowledge. With this improved understanding, we are afforded the opportunity to consider numerous potential therapeutic targets for treating autoimmune disease. As this growing science evolves, we can expect to see the advent of new therapies and new hope for patients who are afflicted with these disorders.

Cutting edge: lupus susceptibility interval Sle3/5 confers responsiveness to prolactin in C57BL/6 mice.

Prolactin is of interest in the pathogenesis of systemic lupus erythematosus (SLE) because almost 25% of SLE patients display hyperprolactinemia, and serum prolactin correlates with disease activity in some patients. Furthermore, hyperprolactinemia causes early mortality in lupus-prone mice and induces a lupus-like phenotype in nonspontaneously autoimmune mice. We show here that the immunomodulatory effects of prolactin are genetically determined; hyperprolactinemia breaks B cell tolerance and causes a lupus-like serology in BALB/c mice expressing a transgene encoding the H chain of an anti-DNA Ab but not in C57BL/6 transgenic mice. In C57BL/6 mice that express both the H chain transgene and the lupus susceptibility interval Sle3/5, prolactin induces increased serum titers of anti-DNA Ab and glomerular Ig depositions. The increase in costimulation due to prolactin-mediated up-regulation of both CD40 on B cells and CD40L on T cells would appear to play a central role in lupus induction in this model.

Combined Autoimmune Disease in a Patient with AIDS

Abstract Immune dysregulation in HIV-infected patients, along with the new medications for treatment of AIDS that possess immunomodulating potential, may lead to an increased incidence of autoimmune diseases in this patient population. However, the presence of combined autoimmune diseases in an AIDS patient is rare. Relapsing polychondritis (RP) is an uncommon inflammatory disease manifested by recurrent attacks of auricular chondritis. The presence of type II and IX collagen antibodies, and their association with HLA-DR4 and other autoimmune diseases, suggests that antiself reactions may be present. Sarcoidosis is a granulomatous disease manifested by inflammation of the lungs, eyes and joints. In the peripheral blood there is depressed cellular immunity and enhanced humoral immunity. We here describe a case of coexisting RP and sarcoidosis in an AIDS patient.