Downregulation of NF-kappaB activity associated with alteration in proliferative response in the spleen after burn injury

Overactivation of mitogen-activated protein kinase and suppression of mitofusin-2 expression are two independent events in high mobility group box 1 protein-mediated T cell immune dysfunction

High mobility group box 1 protein (HMGB1), a critical proinflammatory cytokine, has recently been identified to be an immunostimulatory signal involved in sepsis-related immune dysfunction when released extracellularly, but the potential mechanism involved remains elusive. Here, we showed that the treatment with HMGB1 in vitro inhibited T lymphocyte immune response and expression of mitofusin-2 (Mfn-2; a member of the mitofusin family) in a dose- and time-dependent manner. Upregulation of Mfn-2 expression attenuated the suppressive effect of HMGB1 on T cell immune function. The phosphorylation of both extracellular signal-regulated kinase (ERK)1/2 and p38 mitogen-activated protein kinase (MAPK) was markedly upregulated by treating with high amount of HMGB1, while pretreatment with ERK1/2 and p38 MAPK-specific inhibitors (U0126 and SB203580) could attenuate suppression of T cell immune function and nuclear factor of activated T cell (NFAT) activation induced by HMGB1, respectively. HMGB1-induced activity of ERK1/2 and p38 was not fully inhibited in the presence of U0126 or SB203580. Interestingly, overexpression of Mfn-2 had no marked effect on HMGB1-mediated activation of MAPK, but could attenuate the suppressive effect of HMGB1 on the activity of NFAT. Thus, the mechanisms involved in HMGB1-induced T cell immune dysfunction in vitro at least partly include suppression of Mfn-2 expression, overactivation of ERK1/2, p38 MAPK, and intervention of NFAT activation, while the protective effect of Mfn-2 on T cell immune dysfunction induced by HMGB1 is dependent on other signaling pathway associated with NFAT, but not MAPK. Taken together, we conclude that overactivation of MAPK and suppression of Mfn-2 expression are two independent events in HMGB1-mediated T cell immune dysfunction.

The Effect of Tumor Necrosis Factor-α-Induced Protein 8 Like-2 on Immune Response of CD4+T Lymphocytes in Mice after Thermal Injury

The status of cellular immunity has been shown to be associated with the occurrence and development of sepsis. Accumulating evidence has demonstrated that tumor necrosis factor-α-induced protein 8 like-2 (TIPE2) plays an important role in maintaining homeostasis of immune function. The present study, with the use of a controlled in vivo approach, demonstrated the effect of TIPE2 on cell-mediated immunity of CD4+ T lymphocytes in thermal injury murine model. One hundred and twenty-eight male mice were randomly allocated into four groups, which were sham burn group (n=48), burn group (n=48), burn with lentivirus-RNAi-TIPE2 transfection group (n=16), burn with negative control transfection group (n=16), and they were sacrificed at the designated time points. CD4+ T lymphocytes were isolated from the spleen using MACS microbeads. Phenotypes were analyzed by flow cytometry analysis, and cytokines were determined using ELISA kits. We found that the expression of TIPE2 was markedly increased in CD4+T lymphocytes in mice at 24,48 and 72 hours postburn. Down-regulation of TIPE2 by lentivirus-RNAi-TIPE2 attenuated the suppressive effect of CD4+T lymphocytes, which was associated with profound elevation of nuclear factor of activated T cell (NF-AT) activity. These results demonstrate that TIPE2 appear to be involved in the immune regulation of CD4+ T lymphocytes, and the decrease in TIPE2 expression on CD4+T lymphocytes in vivo can enhance peripheral T lymphocyte function after thermal injury. These data might provide a valid strategy to prevent the development of immunosuppressive state resulted from major burns.

Association between high-mobility group box-1 protein release and immune function of dendritic cells in thermal injury

The present study was performed to investigate in vivo the effect of high-mobility group box-1 protein (HMGB1) on the maturation of dendritic cell (DC) and the influence on T-cell-mediated immunity after thermal injury. Rats were randomly divided into 3 groups as follows: sham burn group, burn group, and burn with ethyl pyruvate (EP) treatment group, and they were sacrificed on post burn days (PBD) 1, 3, 5, and 7 respectively. MACS microbeads were used to isolate splenic DCs and column of nylon wool to obtain T cells. Phenotypes were analyzed by flow cytometry and cytokines were determined with ELISA kits. The expression levels of splenic HMGB1 were significantly elevated during PBD 1-7. DC expressed similar CD80 levels, strongly enhanced CD86, and slightly elevated MHC class II levels in comparison to DC from sham-injured rats, and protein levels of IL-12 were not increased after thermal injury. Administration of EP to inhibit HMGB1 could significantly enhance expression levels of CD80, MHC class II on DC surface, and IL-12 production after burns. Simultaneously, proliferative activity and expression levels of IL-2 as well as IL-2R alpha of T cell were restored. These results suggested that the excessively released HMGB1 might stimulate splenic DC to mature abnormally and down-regulate the IL-12 production, and further shifting of Th1 to Th2 with suppression of T-lymphocyte immune function following burn injury.

The effect of high-mobility group box 1 protein on activity of regulatory T cells after thermal injury in rats

The aim of the present study was to investigate in vivo the effect of high-mobility group box 1 protein (HMGB1) on activity of regulatory T cells (Tregs) and the influence on T-cell-mediated immunity after thermal injury. Male Wistar rats were randomly divided into four groups as follows: sham burn group, burn group, burn with ethyl pyruvate treatment group, and burn with antireceptor for advanced glycation end products (RAGE) antibody treatment group, and they were killed on postburn days 1, 3, 5, and 7, respectively, with eight animals at each time point. Magnetic cell sorting microbeads were used to isolate splenic Tregs and a column of nylon wool to obtain T cells. Phenotypes, including cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), forkhead/winged helix transcription factor p3 (Foxp3), RAGE, and IL-2Ralpha, were analyzed by flow cytometry. Levels of HMGB1, IL-10, IL-2, IL-4 and interferon gamma were determined by enzyme-linked immunosorbent assay kits, and real-time reverse transcription-polymerase chain reaction was performed to detect mRNA expression of IL-10, IL-2, and IL-2Ralpha. Serum HMGB1 levels were significantly elevated during postburn days 1 to 7. In the burn group, CTLA-4 and Foxp3 expression levels of Tregs were strongly enhanced in comparison to the sham-injured group, and the capacity of Tregs to produce IL-10 was markedly increased. Administration of ethyl pyruvate to inhibit HMGB1 or anti-RAGE antibody could significantly decrease expression levels of CTLA-4, Foxp3 on Tregs, and IL-10 production after burns. Simultaneously, proliferative activity and expression levels of IL-2 and IL-2Ralpha of T cell were restored. The excessively released HMGB1 might stimulate CD4+CD25+Treg activity via binding RAGE on the surface of Tregs and trigger a shift of T(H)1 to T(H)2 with suppression of T-lymphocyte immune function after burn injury.

Relationship between high-mobility group box 1 protein release and T-cell suppression in rats after thermal injury

To study whether high-mobility group box 1 protein (HMGB1) has an effect on T-cell-mediated immunity secondary to burn injury, 96 male Wistar rats weighing 250 to 300 g were randomly divided into three groups as follows:sham burn group, burn group, and burn with ethyl pyruvate treatment group, and they were killed on postburn days (PBDs)1, 3, 5, and 7, respectively, with 8 animals at each time point. Columns of nylon wool were used to isolate splenic T cells. T-Cell proliferation was analyzed with thiazolyl blue and expression of IL-2 receptor alpha (IL-2Ralpha) on the surface of T cell with flow cytometry. Levels of HMGB1 were determined using Western blot analysis. IL-2, soluble IL-2R, IL-4, and interferon-gamma were determined with enzyme-linked immunosorbent assay kits. Gene expressions of HMGB1, IL-2, and IL-2R were assessed using reverse-transcription polymerase chain reaction, and activation of nuclear factor of activated T cell was determined with gel mobility shift assay. The levels of HMGB1 in plasma were significantly elevated on PBDs 1 to 5. Significant proliferation of splenic T cells and IL-2, as well as IL-2Ralpha expression on T cells, were simultaneously suppressed to a certain extent on PBDs 1 to 7. Nuclear factor of activated T-cell activity of splenic T cells was markedly down-regulated on PBDs 1 to 3. Administration of ethyl pyruvate to inhibit HMGB1 can significantly restore proliferative activity, nuclear factor of activated T-cell activity, and expression levels of IL-2 and IL-2Ralpha on T cells. High-mobility group box 1 protein released after major burns might be associated with the pathogenesis of immunosuppression in splenic T lymphocytes in rats.

Effect of bacterial infection on expression of NF-κBP65 after preserved splenic operation in rabbits using microwave coagulation

AIM: To investigate effect and significance of bacterial infection on expression of NF-κBP65 after partial splenectomy of rabbits using microwave coagulation.

METHODS: Japanese white rabbits with large ears were randomly divided into two groups. There were sham group and experiment group,which was alse called partial splenectomy group of rabbits using microwave coagulation. Streptococcus pneumonia suspension was injected into ear veins 1 month after partial splenectomy of rabbits using microwave coagulation and sham operation group. During 48 hours the animal life was observed. The splenic samples weighted and NF-κBP65 count index of expression of residual spleen was detected.

RESULTS: At 48 hours after bacterial injection no rabbit died in two groups. There was no significant difference between splenic qualiyies of two groups. Under microscope the fibrosis was showed in remnant end of spleen coagulated by microwave. NF-κBP65 was mainly stained in cytoplasm or nucleolus. There was no significance difference between NF-κBP65 count index of expression in experiment group and sham group.

CONCLUSION: Splenic injury coagulated by microwave may be restored in short term. Preserved splenic operation using microwave coagulation is a certainly valuable method of operation.

CD14-dependent modulation of NF-κB alternative splicing in the lung after burn injury

Nuclear factor kappa-B (NF-kappaB), a key downstream player of the LPS signaling pathway, has been shown to undergo alternative splicing in in vitro studies. In this study, we examined the effect of injury and the role of CD14 on NF-kappaB alternative splicing using a murine burn model. CD14 knockout and respective wild-type mice were sacrificed after 18% total body surface area burn. RT-PCR and subsequent sequencing analysis revealed that injury induced multiple novel splicing variants of relA, relB, and NF-kappaB2 in the lungs of CD14 knockout but not wild-type mice. These novel variants resulted either from exon skipping, alternative usage of splicing signals, or intron retention. All but one variant resulted in a frameshift leading to premature termination of translation. These splicing variants encoded for proteins that lacked the domains essential for NF-kappaB transcription factor functions. Two NF-kappaB2 variants acquired only minor changes in their C-terminus that might affect their post-translational cleavage into active isoforms. These results suggest that alternative splicing may be one of the mechanisms by which NF-kappaB activity in the lungs can be regulated after injury. Furthermore, the CD14-mediated LPS signaling pathway may play a role in the regulation of NF-kappaB alternative splicing in the lungs after injury.