Clearance deficiency and systemic lupus erythematosus (SLE)

APS--more systemic disease than SLE

The antiphospholipid syndrome is a systemic autoimmune disease that can have serious consequences for patients. Importantly, there is a wide range of clinical presentations. In this issue we have attempted to provide an overview of these features and place it in the context of autoimmunity.

Secondary necrosis in multicellular animals: an outcome of apoptosis with pathogenic implications

In metazoans apoptosis is a major physiological process of cell elimination during development and in tissue homeostasis and can be involved in pathological situations. In vitro, apoptosis proceeds through an execution phase during which cell dismantling is initiated, with or without fragmentation into apoptotic bodies, but with maintenance of a near-to-intact cytoplasmic membrane, followed by a transition to a necrotic cell elimination traditionally called “secondary necrosis”. Secondary necrosis involves activation of self-hydrolytic enzymes, and swelling of the cell or of the apoptotic bodies, generalized and irreparable damage to the cytoplasmic membrane, and culminates with cell disruption. In vivo, under normal conditions, the elimination of apoptosing cells or apoptotic bodies is by removal through engulfment by scavengers prompted by the exposure of engulfment signals during the execution phase of apoptosis; if this removal fails progression to secondary necrosis ensues as in the in vitro situation. In vivo secondary necrosis occurs when massive apoptosis overwhelms the available scavenging capacity, or when the scavenger mechanism is directly impaired, and may result in leakage of the cell contents with induction of tissue injury and inflammatory and autoimmune responses. Several disorders where secondary necrosis has been implicated as a pathogenic mechanism will be reviewed.

Anti-mitochondrial antibody-negative primary biliary cirrhosis

The recent development in the authors' laboratory of a sensitive bead assay able to detect AMA in 20% of otherwise AMA-negative sera seems to support the hypothesis that many AMA-negative cases of primary biliary cirrhosis (PCB) are secondary to limits in the methods used and do not represent an independent clinical entity. Clinical data demonstrate that patients without detectable serum AMA do not differ in their natural history from their seropositive counterparts. Anti-nuclear antibodies have been associated repeatedly with more severe disease and are helpful tools in the management of patients who have PBC, particularly those lacking AMA.

High-mobility group box 1 (HMGB1) protein at the crossroads between innate and adaptive immunity

Tissue damage occurs often in the life of mammals and is usually repaired. Dying cells are swiftly phagocytosed, but before disappearing, they alert surrounding cells to activate homeostatic programs. They release signals that recruit inflammatory cells to the site of injury, promote cell migration and cell division to replace dead cells, and activate the immune system in anticipation of microbial invasion. Many of these events involve high-mobility group box 1 protein (HMGB1), a nuclear protein that is released passively when necrotic cells lose the integrity of their membranes. HMGB1 behaves as a trigger of inflammation, attracting inflammatory cells, and of tissue repair, recruiting stem cells and promoting their proliferation. Moreover, HMGB1 activates dendritic cells (DCs) and promotes their functional maturation and their response to lymph node chemokines. Activated leukocytes actively secrete HMGB1 in the microenvironment. Thus, HMGB1 acts in an autocrine/paracrine fashion and sustains long-term repair and defense programs. DCs secrete HMGB1 several hours after contact with the first maturation stimulus; HMGB1 secretion is critical for their ability to reach the lymph nodes, to sustain the proliferation of antigen-specific T cells, to prevent their activation-dependent apoptosis, and to promote their polarization towards a T-helper 1 phenotype. These immune responses will also be directed against self-antigens that DCs process at the time of injury and can lead to autoimmunity.

Infusion of UVB-treated splenic stromal cells induces suppression of beta cell antigen-specific T cell responses in NOD mice

Our previous study has demonstrated that transfusion of UVB-irradiation-induced apoptotic beta cells effectively prevents type 1 diabetes (T1D) in non-obese diabetic (NOD) mice. However, the limitation of beta cell source would preclude the clinical application of this approach. Therefore, in the present study, we have attempted to establish a more practical approach by utilizing apoptotic non-beta cells to prevent T1D. We find that apoptotic splenic stromal cells significantly suppress beta cell antigen-reactive T cell proliferation in vitro and in vivo. Moreover, beta cell antigen-specific T cells primed by beta cell antigens in the presence of apoptotic stromal cells have markedly reduced responsiveness to the re-stimulation of the same beta cell antigen. We also find that beta cell antigen-specific IL-10-producing CD4+ T cells are induced in the presence of apoptotic splenic stromal cells. As expected, transfusion of apoptotic stromal cells effectively protected NOD mice from developing T1D. Furthermore, the proliferation of adoptively transferred beta cell antigen-specific TCR-transgenic T cells in pancreatic draining lymph nodes is markedly suppressed in UVB-stroma-treated mice, indicating that UVB-stroma treatment induces immune tolerance to multiple beta cell antigens. This study provides an effective and convenient approach for managing T1D by utilizing apoptotic non-beta cells.

Estrogen distinctively modulates spleen DC from (NZB x NZW) F1 female mice in various disease development stages

Estrogen is important in the pathogenesis of systemic lupus erythematosus (SLE). The modulation of estrogen on dendritic cells (DCs) may involve in SLE development. Our purpose was to find out whether in vitro the effect of estrogen on DCs is correlated with the disease progression in vivo. We compared the effects of 17beta-estradiol (E2) on spleen DCs from SLE murine model-(NZB x NZW) F1 female mice before and after the disease onset. Results showed that E2 changed the surface molecule CD40, cytokines IL-6, IL-10, IL-12 and TNFalpha and stimulatory ability of spleen DCs from the mice. Selective estrogen receptor modulator-tamoxifen (TAM) could antagonize E2 effects and E2 could influence estrogen receptor (ER alpha) level in DCs. The changes of DCs from various age old mice were different even contrast. So E2 participates in SLE through modulating DCs by binding ER alpha. The effects of E2 on DCs from mice in various disease progression stages were different.

Anti-CD16 autoantibodies and delayed phagocytosis of apoptotic cells in primary biliary cirrhosis

Primary biliary cirrhosis is characterized by chronic hepatic inflammation and immune mediated apoptosis of bile duct epithelial cells. Delayed macrophage phagocytosis of opsonized apoptotic cells, noted in other autoimmune diseases, may promote inflammation. Recent studies suggest serum anti-CD16 autoantibodies contribute to impaired macrophage phagocytosis by blocking complement receptor 3 (CR3) signaling via CD16. Therefore, serum anti-CD16 levels and the ability of monocyte derived macrophages from individuals with PBC to phagocytosis apoptotic cells were compared to controls. The mean level of anti-CD16 IgM autoantibodies (0.86+/-0.62 v. 0.35+/-0.22, respectively, p=0.031) was increased in PBC compared to control sera, and mean PBC phagocytosis of opsonized apoptotic cells was significantly decreased compared to controls (23.9+/-12.2% v. 43.9+/-14.4%, respectively, p=0.020). However, PBC phagocytosis of opsonized apoptotic cells was not significantly affected by the presence or absence of autologous serum (20.8+/-13.5% v. 23.9+/-12.2%, respectively, p=0.560). PBC phagocytosis of opsonized apoptotic cells inversely correlated with CD16 (and CR3) expression levels on Day 5 after culture in the presence or absence of autologous serum (r=-0.546, p=0.033 and r=-0.519, p=0.042, respectively). Phagocytosis of non-opsonized apoptotic cells did not correlate with CD16 or CR3 expression (p>0.050). In conclusion, PBC macrophage phagocytosis of opsonized apoptotic cells is impaired, irrespective of serum factors and may increase hepatic inflammation.

A quantitative comparison of rates of phagocytosis and digestion of apoptotic cells by macrophages from normal (BALB/c) and diabetes-prone (NOD) mice

Macrophages play an important role in clearing apoptotic debris from tissue. Defective or reduced clearance, seen, for instance, in non-obese diabetic (NOD) mice, has been correlated with initiation of autoimmune (Type 1) diabetes (T1D) (O'Brien BA, Huang Y, Geng X, Dutz JP, Finegood DT. Diabetes 51: 2481-2488, 2002). To validate such a link, it is essential to quantify the reduced clearance (for example, by comparison to BALB/c control mice) and to determine which elements of that clearance are impaired. Recently, we fit data for the time course of in vitro macrophage feeding experiments to basic models of macrophage clearance dynamics, thus quantifying kinetics of uptake and digestion of apoptotic cells in both mouse strains (Marée AFM, Komba M, Dyck C, Łabeçki M, Finegood DT, Edelstein-Keshet L. J Theor Biol 233: 533-551, 2005). In the cycle of modeling and experimental investigation, we identified the importance of 1) measuring short-, intermediate-, and long-time data (to increase the accuracy of parameter fits), and 2) designing experiments with distinct observable regimes, including engulfment-only and digestion-only phases. Here, we report on new results from experiments so designed. In comparing macrophages from the two strains, we find that NOD macrophage engulfment of apoptotic cells is 5.5 times slower than BALB/c controls. Significantly, our new data demonstrate that digestion is at least two times slower in NOD, in contrast with previous conclusions. Moreover, new data enable us to detect an acceleration in engulfment (after the first engulfment) in both strains, but much smaller in NOD macrophages.

The role of the innate immune response in autoimmune disease

Autoimmune diseases are the clinical correlate of a dysregulation of the immune system, involving multiple steps and multiple components of both the innate and the adaptive immune system. Innate immune cells are sensitive to a very limited repertoire of foreign "patterns" that bind to selective "pattern recognition receptors". In contrast, adaptive auto-reactive T or B cells bear receptors specific for antigens including "self" antigens and are rendered non-reactive by several "quality control" mechanisms. Under special conditions, activation of cells of the innate immune system can break the state of inactivity of auto-reactive cells of the adaptive immune system, thereby provoking autoimmune disease. Here we review examples to illustrate how innate immune activation influences autoimmune disease and point to the implications for the treatment of human autoimmune disease.

Autophagy: highlighting a novel player in the autoimmunity scenario

Autophagy is a physiological cellular mechanism that degrades and recycles proteins and other molecules to maintain an adequate amino acid level during nutritional starvation of the cell. Autophagy is involved in cellular homeostasis and differentiation, as well as in tissue remodeling, aging, cancer, and other diseases. Under particular environmental conditions, autophagy can also be a contributor to programmed cell death, or can act as a defense mechanism for the elimination of intracellular bacteria and viruses. According to recent experimental data, autophagy may be implicated in autoimmunity by promotion of major histocompatibility complex (MHC) class II presentation of cytosolic antigens and control of T lymphocyte homeostasis, and its induction by Th1 cytokines and perhaps by specific serum autoantibodies. We review herein the role of autophagy in immune function and its possible contribution to breakdown of tolerance and development of autoimmunity.

Analysis of expression and function of the inhibitory receptor ILT2 (CD85j/LILRB1/LIR-1) in peripheral blood mononuclear cells from patients with systemic lupus erythematosus (SLE)

The aim of this work was to study the expression and function of the inhibitory receptor ILT2/CD85j in peripheral blood mononuclear cells (PBMC) from patients with systemic lupus erythematosus (SLE). We studied 23 SLE patients as well as 17 patients with rheumatoid arthritis, 10 with fibromyalgia, and 23 healthy individuals. We found a variable level of expression of ILT2 in the PBMC from both SLE patients and controls, with no significant differences among them. However, when the expression of this receptor was assessed in cell subsets, significantly lower levels were detected in CD19+ lymphocytes from SLE patients compared with healthy controls. Functional assays performed in unfractionated PBMC, showed a significant diminished inhibitory activity of ILT2 in CD4+ and CD8+ cell subsets from SLE patients compared to either rheumatoid arthritis or fibromyalgia patients, and healthy individuals. Our results show that the PBMC from some patients with SLE show a defective expression of ILT2, and that most of them exhibit a poor function of this inhibitory receptor.