Emerging concepts for sexual predilection in the disease systemic lupus erythematosus

Elevated Serum Lysophosphatidylcholine in Patients with Systemic Lupus Erythematosus Impairs Phagocytosis of Necrotic Cells In Vitro

Objectives

Impaired clearance of dying and dead cells by professional and amateur phagocytes plays a crucial role in the etiology of systemic lupus erythematosus (SLE). While dying, cells expose and release a plethora of eat-me and find-me signals to ensure their timely removal before entering the dangerous stage of secondary necrosis. A well-described chemoattractant for macrophages is dying cell-derived lysophosphatidylcholine (LPC). However, its implications for and/or its association with SLE disease, so far, have not been examined. In the present study, we analyzed the LPC serum concentrations of patients with SLE and rheumatoid arthritis (RA). Subsequently, we examined if and to which extent the measured serum concentrations of LPC and an LPC-rich environment can impact the phagocytosis of necrotic cells.

Methods

Sera from patients with SLE, RA, and normal healthy donors (NHD) were characterized for several parameters, including LPC concentrations. Phagocytosis of dead cells by human macrophages in the presence of SLE and NHD sera was quantified. Additionally, the impact of exogenously added, purified LPC on phagocytosis was analyzed.

Results

Patients with SLE had significantly increased LPC serum levels, and high serum LPC of SLE patients correlated significantly with impaired phagocytosis of dead cells in the presence of heat-inactivated serum. Phagocytosis in the presence of sera from NHD showed no correlation to LPC levels, but exogenous addition of purified LPC in the range as measured in SLE patients’ sera led to a concentration-dependent decrease.

Conclusion

Our data show that high levels of LPC as observed in the sera of SLE patients have a negative impact on the clearance of dead cells by macrophages. Chemoattraction requires a concentration gradient. The higher the LPC concentration surrounding a dying or dead cell, the smaller the achievable gradient upon LPC release will be. Thus, it is feasible to assume that elevated LPC levels can interfere with the build-up of a local LPC gradient during cell death, and hence might play a role in the establishment and/or perpetuation of SLE disease.

Gender differences in autoimmune disease

Autoimmune diseases are a range of diseases in which the immune response to self-antigens results in damage or dysfunction of tissues. Autoimmune diseases can be systemic or can affect specific organs or body systems. For most autoimmune diseases there is a clear sex difference in prevalence, whereby females are generally more frequently affected than males. In this review, we consider gender differences in systemic and organ-specific autoimmune diseases, and we summarize human data that outlines the prevalence of common autoimmune diseases specific to adult males and females in countries commonly surveyed. We discuss possible mechanisms for sex specific differences including gender differences in immune response and organ vulnerability, reproductive capacity including pregnancy, sex hormones, genetic predisposition, parental inheritance, and epigenetics. Evidence demonstrates that gender has a significant influence on the development of autoimmune disease. Thus, considerations of gender should be at the forefront of all studies that attempt to define mechanisms that underpin autoimmune disease.

Octreotide for the treatment of systemic lupus erythematosus: clinical effects and an in vitro study on its therapeutic mechanism

Increased serum growth hormone (GH), together with high expression of growth hormone receptor on peripheral blood mononuclear cells (PBMCs), correlates with systemic lupus erythematosus (SLE) activity, suggesting that modulation of GH signaling may affect SLE activity. We explored the effects of octreotide (OCT), an analog of somatostatin that suppresses the release of GH, in SLE. The objectives of the study were to investigate effects of OCT on the proliferative capacity and cytokine expression of PBMCs from patients with SLE and to investigate therapeutic effects of OCT in patients with SLE. PBMCs from 13 active/inactive SLE patients and 11 controls were pretreated with or without GH and cultured with OCT. The proliferation of PBMCs was assessed by MTT assay and cytokines were quantified by ELISA. We compared the clinical response of 12 patients with SLE treated with OCT (100 µg twice daily) with 12 patients treated with prednisone over three months. OCT inhibited PBMC proliferation in a dose-dependent manner and decreased the secretion of interleukin-6 (IL-6), interleukin-10 (IL-10), and interferon-gamma (IFN-γ). Patients treated with OCT demonstrated improvements in SLEDAI, dsDNA titer, complement levels, and erythrocyte sedimentation rate (ESR). OCT inhibited PBMC proliferation and PBMC secretion of IL-6, IL-10 and IFN-γ stimulated by GH. Treatment of patients with OCT resulted in clinical improvement in SLE.

Cytokine networks in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease more prominent in women and characterized by multiple organ damage. Imbalance in cytokine production and cytokine levels correlates with SLE progression, making the understanding of SLE cytokine networks very important for SLE treatment strategy and drug development. In this article, we review cytokine networks that may be involved in the pathogenesis of SLE by briefly describing abnormal cytokine production and serum cytokine levels in SLE patients. We also focus on the pathological roles of cytokines and their interactions in immunoregulatory networks and suggest how their disturbances may implicate in pathological conditions in SLE. Finally, we further discuss the influence of estrogen on these cytokine networks.

Autoimmune disease and the female patient

This article focuses on the pathogenesis of the gender gap of autoimmune disease. Specifically, the discussion characterizes the role of sex hormones in the immune response and a female predilection for the common diseases seen in daily practice (ie, lupus erythematosus, myasthenia gravis, and other autoimmune diseases). A comparison between the sexes, with respect to autoimmune disease mechanisms, is presented to give oral and maxillofacial surgeons a better insight as to the role of sex and successful surgical treatment outcomes in this population of patients.

Effects of MHC and gender on lupus-like autoimmunity in Nba2 congenic mice

The lupus-like disease that develops in hybrids of NZB and NZW mice is genetically complex, involving both MHC- and non-MHC-encoded genes. Studies in this model have indicated that the H2d/z MHC type, compared with H2d/d or H2z/z, is critical for disease development. C57BL/6 (B6) mice (H2b/b) congenic for NZB autoimmunity 2 (Nba2), a NZB-derived susceptibility locus on distal chromosome 1, produce autoantibodies to nuclear Ags, but do not develop kidney disease. Crossing B6.Nba2 to NZW results in H2b/z F1 offspring that develop severe lupus nephritis. Despite the importance of H2z in past studies, we found no enhancement of autoantibody production or nephritis in H2b/z vs H2b/b B6.Nba2 mice, and inheritance of H2z/z markedly suppressed autoantibody production. (B6.Nba2 x NZW)F1 mice, compared with MHC-matched B6.Nba2 mice, produced higher levels of IgG autoantibodies to chromatin, but not to dsDNA. Although progressive renal damage with proteinuria only occurred in F1 mice, kidneys of some B6.Nba2 mice showed similar extensive IgG and C3 deposition. We also studied male and female B6.Nba2 and F1 mice with different MHC combinations to determine whether increased susceptibility to lupus among females was also expressed within the context of the Nba2 locus. Regardless of MHC or the presence of NZW genes, females produced higher levels of antinuclear autoantibodies, and female F1 mice developed severe proteinuria with higher frequencies. Together, these studies help to clarify particular genetic and sex-specific influences on the pathogenesis of lupus nephritis.

The Neuroendocrine–Immune Interactions in Systemic Lupus Erythematosus: A Basis for Understanding Disease Pathogenesis and Complexity

Much progress has been made in the understanding of the impact of the neuroendocrine immune interactions and the pathogenic role in systemic lupus erythematosus, clinically and at the molecular level. This article focuses on the intertwining networks that involve the hypothalamic-pituitary-adrenal axis, cytokines within the central nervous system, and the sympathetic system. Hormones (estrogen, prolactin, gonadotropin-releasing hormone, and leptin) play an important role as immunomodulatory agents.

Age-related changes in serum growth hormone, insulin-like growth factor-1 and somatostatin in system lupus erythematosus

BACKGROUND

Systemic lupus erythematosus is an age- and gender-associated autoimmune disorder. Previous studies suggested that defects in the hypothalamic/pituitary axis contributed to systemic lupus erythematosus disease progression which could also involve growth hormone, insulin-like growth factor-1 and somatostatin function. This study was designed to compare basal serum growth hormone, insulin-like growth factor-1 and somatostatin levels in female systemic lupus erythematosus patients to a group of normal female subjects.

METHODS

Basal serum growth hormone, insulin-like growth factor-1 and somatostatin levels were measured by standard radioimmunoassay.

RESULTS

Serum growth hormone levels failed to correlate with age (r2 = 3.03) in the entire group of normal subjects (i.e. 20 - 80 years). In contrast, serum insulin-like growth factor-1 levels were inversely correlated with age (adjusted r2 = 0.092). Of note, serum growth hormone was positively correlated with age (adjusted r2 = 0.269) in the 20 - 46 year range which overlapped with the age range of patients in the systemic lupus erythematosus group. In that regard, serum growth hormone levels were not significantly higher compared to either the entire group of normal subjects (20 - 80 yrs) or to normal subjects age-matched to the systemic lupus erythematosus patients. Serum insulin-like growth factor-1 levels were significantly elevated (p < 0.001) in systemic lupus erythematosus patients, but only when compared to the entire group of normal subjects. Serum somatostatin levels differed from normal subjects only in older (i.e. >55 yrs) systemic lupus erythematosus patients.

CONCLUSIONS

These results indicated that systemic lupus erythematosus was not characterized by a modulation of the growth hormone/insulin-like growth factor-1 paracrine axis when serum samples from systemic lupus erythematosus patients were compared to age- matched normal female subjects. These results in systemic lupus erythematosus differ from those previously reported in other musculoskeletal disorders such as rheumatoid arthritis, osteoarthritis, fibromyalgia, diffuse idiopathic skeletal hyperostosis and hypermobility syndrome where significantly higher serum growth hormone levels were found. Somatostatin levels in elderly systemic lupus erythematosus patients may provide a clinical marker of disease activity in these patients.