[An impaired detection and clearance of dying cells can lead to the development of chronic autoimmunity]

SUMO modification in apoptosis

Apoptosis and clearance of dead cells is highly evolutionarily conserved from nematode to humans, which is crucial to the growth and development of multicellular organism. Fail to remove apoptotic cells often lead to homeostasis imbalance, fatal autoimmune diseases, and neurodegenerative diseases. Small ubiquitin-related modifiers (SUMOs) modification is a post-translational modification of ubiquitin proteins mediated by the sentrin-specific proteases (SENPs) family. SUMO modification is widely involved in many cellular biological process, and abnormal SUMO modification is also closely related to many major human diseases. Recent researches have revealed that SUMO modification event occurs during apoptosis and clearance of apoptotic cells, and plays an important role in the regulation of apoptotic signaling pathways. This review summarizes some recent progress in the revelation of regulatory mechanisms of these pathways and provides some potential researching hotpots of the SUMO modification regulation to apoptosis.

Daidzein enhances efferocytosis via transglutaminase 2 and augmentation of Rac1 activity

Clearance of apoptotic cells, termed "efferocytosis", is the mechanism required to prevent secondary necrosis and release of proinflammatory cytokines. Defective efferocytosis is cumulatively regarded as one of mechanisms in the development of autoimmune and chronic inflammatory diseases. Our previous finding showed that ethanolic extract from Glycine tomentella Hayata (GTH) can enhance mouse macrophage RAW264.7 efferocytosis (clearance of apoptotic cells). We have demonstrated that the major components of GTH are daidzein, catechin, epicatechin and naringin. Here, we explore the potential of each component in modulating efferocytic capability. For this, RAW264.7 cells were cultured with CFDA-stained apoptotic cells and assayed by flow cytometry. We found that daidzein is the main component of GTH, and it can enhance RAW264.7 efferocytosis dose-dependently. Moreover, the enhancive effect of daidzein on macrophage efferocytic capability is accompanied by increased transglutaminase 2 (TG2) at both mRNA and protein levels. TG2 knockdown attenuated daidzein increased macrophage efferocytic capability. After treatment with daidzein, increased phosphorylation was observed in Erk, but not in p38 and JNK. Finally, we report that after daidzein treatment, Rac1 activity was markedly increased and the mitochondrial membrane potential was decreased, which may contribute to efferocytosis. Taken together, these data suggest that enhancement of macrophage efferocytic capability by daidzein treatment was mainly through up-regulation of TG2 expression and Rac1 activity. Daidzein may have the therapeutical potential in the treatment of inflammatory diseases.

The healing of tibial fracture and response of the local lymphatic system

BACKGROUND

Damage of tissues by mechanical injury and inflammation is followed by reaction of the regional lymphoid tissue, lymphatics, and lymph nodes. In our previous lymphoscintigraphic studies, we showed that closed fractures of a lower limb cause reaction of the local lymphoid tissue. There was dilation of lymphatics draining the site of the fracture and enlargement of inguinal lymph nodes. These changes persisted even after clinical healing of the fracture. In the long-lasting nonhealing fractures, the lymphoscintigraphic pictures were different. The draining lymphatics became obliterated, and the lymph nodes disappeared.

METHODS

In this study, we tried to correlate the lymphoscintigraphic images, reflecting the immune events at the fracture site, with the immunohistochemical observations of the biopsy specimens obtained during corrective operations from the healing and nonhealing fracture gaps. Thirty-eight patients with closed fracture of the tibia without traumatic skin changes were studied.

RESULTS

We confirmed that closed tibial fracture evokes response of the regional lymphatic system. Normal fracture healing with immune cell infiltrates and foci of ossification was accompanied by dilated lymphatics and enlarged lymph nodes. Prolonged nonhealing fracture with lack of cellular reaction in the gap proceeded with decreased mass of lymph nodes.

CONCLUSION

This study provides evidence for existence of a functional axis between wound of bone and surrounding soft tissue and the local lymphatic (immune) system. We hypothesize that the fast healing is regulated by influx into the wound of lymph node regulatory cells, whereas prolonged healing causes gradual exhaustion of the regional lymph node functional elements, and reciprocally impairment in sending regulatory cells to the fracture gap.

Superoxide anion production by neutrophils is associated with prevalent clinical manifestations in systemic lupus erythematosus

To determine the relation between neutrophil function and the clinical characteristics of systemic lupus erythematosus (SLE), the superoxide anion (O2-) production by neutrophils, mediated by FcgammaR and FcgammaR/CR cooperation, was studied in 64 SLE patients classified according to their prevalent clinical manifestations. Three clinically distinct patterns were designated: (1) manifestations associated with the occurrence of cytotoxic antibodies (SLE-I group); (2) manifestations associated with circulating immune complexes (IC; SLE-II group), and (3) manifestations associated with IC and cytotoxic antibodies (SLE-III group). O2- production was evaluated by a lucigenin-dependent chemiluminescent assay in neutrophils stimulated with IC-IgG opsonized or not with complement. No difference in O2- production was observed when neutrophil responses from healthy controls were compared to the unclassified patients. However, when the SLE patient groups were considered, the following differences were observed: (1) SLE-I neutrophils showed lower O2- production mediated by the IgG receptor (FcgammaR) with the cooperation of complement receptors (FcgammaR/CR) than observed in the SLE-II, SLE-III, and healthy groups; (2) neutrophils from the SLE-II group showed a decreased [Formula: see text] production mediated by FcgammaR/CR compared to the SLE-III group, (3) SLE-III neutrophils produced more O(2)(-) than neutrophils from the SLE-II and control groups, and (4) CR showed inefficiency in mediating the O2- production by neutrophils from the SLE-I group. Comparative experiments on the kinetics of chemiluminescence (CL; Tmax and CLmax) disclosed differences only for the SLE-I group. Taken together, these results suggest that differences in oxidative metabolism of neutrophils mediated by FcgammaR/CR may reflect an acquired characteristic of disease associated with distinct clinical manifestations.

Antigen-induced B cell apoptosis is independent of complement C4

Deficiencies in early complement components are associated with the development of systemic lupus erythematosus (SLE) and therefore early complement components have been proposed to influence B lymphocyte activation and tolerance induction. A defect in apoptosis is a potential mechanism for breaking of peripheral B cell tolerance, and we hypothesized that the lack of the early complement component C4 could initiate autoimmunity through a defect in peripheral B lymphocyte apoptosis. Previous studies have shown that injection of a high dose of soluble antigen, during an established primary immune response, induces massive apoptotic death in germinal centre B cells. Here, we tested if the antigen-induced apoptosis within germinal centres is influenced by early complement components by comparing complement C4-deficient mice with C57BL/6 wild-type mice. We demonstrate that after the application of a high dose of soluble antigen in wild-type mice, antibody levels declined temporarily but were restored almost completely after a week. However, after antigen-induced apoptosis, B cell memory was severely limited. Interestingly, no difference was observed between wild-type and complement C4-deficient animals in the number of apoptotic cells, restoration of antibody levels and memory response.

[The apoptosis marker enzyme poly-(ADP-ribose) polymerase (PARP) in systemic lupus erythematosus]

The enzyme poly-(ADP-ribose) polymerase (PARP) is localized within the cell nucleus and catalyzes DNA-repair. During programmed cell death (apoptosis), PARP is enzymatically cleaved. Detection of the cleavage products is characteristic for apoptosis. In patients with systemic lupus erythematosus (SLE), the highly ordered signal transduction cascade of apoptosis is disturbed. SLE patients show reduced PARP activity . PARP cleavage products are mainly found in association with either antinuclear and/or anti-dsDNA antibodies. In addition, serum samples from SLE patients and other autoimmune diseases display anti-PAR and anti-PARP autoantibodies.

Phagocytosis of apoptotic cells and immune regulation

The termination of the apoptotic programme occurs in most cases via recognition and clearance by phagocytes, especially the professional phagocytes, such as macrophages and immature dendritic cells. Engulfed cells do not simply disappear from the midst of living tissues. The fine-defined presentation of yielded self-antigens to T cells is a central event in the induction or the maintenance of the peripheral immune tolerance to self. Conversely, abnormality in this pathway may contribute to the pathogenesis of systemic and organ-specific autoimmune diseases. We herein reviewed the relationship between phagocytosis of apoptotic cells and immune regulation, especially the effects of engulfed apoptotic cells on immune tolerance and autoimmune diseases.