CD137: costimulator turns suppressor?

CD137: A Member of the TNFR Family - in Psoriasis Skin Lesions in Comparison with Normal Skin Specimens

Background & Objective

CD137 is a member of the TNF-Receptor family. TNF-alpha antagonists have therapeutic effect in active psoriasis. In this study, the relative frequency of CD137 expression was investigated in the inflammatory cells of psoriasis lesions for the first time.

Methods

The specimens were obtained from pathology department of Al-Zahra hospital from paraffin-embedded skin specimens collected from 2007 till 2016. . A total number of f 64 psoriasis skin specimens and 34 normal skin specimens were reviewed for the diagnosis. Then, the immunohistochemical staining for CD137, CD4, and CD8 was performed.

Results

CD137 expression of dermal inflammatory cells in psoriasis lesions was 11.19±5.5%. Although, in normal skin tissues, CD137 expression was observed in 1.3±3.03% of the inflammatory cells. (P=0.001). The relative frequency of the CD137 positive inflammatory cells was significantly higher in the epidermis compared to dermis (epidermis: 31.1%±12.8, dermis 11.1%±5.5). There was no remarkable relation between the CD137 expression rate and the CD4: CD8 ratio.

Conclusion

CD137 as a TNF-alpha receptor has a significant role in pathogenesis of the psoriasis lesions. Therefore, CD137 antagonists can be considered as a novel target for the treatment of incurable psoriasis patients.

Effect of oxygen-breathing during a decompression-stop on bubble-induced platelet activation after an open-sea air dive: oxygen-stop decompression

PURPOSE

We highlighted a relationship between decompression-induced bubble formation and platelet micro-particle (PMP) release after a scuba air-dive. It is known that decompression protocol using oxygen-stop accelerates the washout of nitrogen loaded in tissues. The aim was to study the effect of oxygen deco-stop on bubble formation and cell-derived MP release.

METHODS

Healthy experienced divers performed two scuba-air dives to 30 msw for 30 min, one with an air deco-stop and a second with 100% oxygen deco-stop at 3 msw for 9 min. Bubble grades were monitored with ultrasound and converted to the Kisman integrated severity score (KISS). Blood samples for cell-derived micro-particle analysis (AnnexinV for PMP and CD31 for endothelial MP) were taken 1 h before and after each dive.

RESULTS

Mean KISS bubble score was significantly lower after the dive with oxygen-decompression stop, compared to the dive with air-decompression stop (4.3 ± 7.3 vs. 32.7 ± 19.9, p < 0.001). After the dive with an air-breathing decompression stop, we observed an increase of the post-dive mean values of PMP (753 ± 245 vs. 381 ± 191 ng/μl, p = 0.003) but no significant change in the oxygen-stop decompression dive (329 ± 215 vs. 381 +/191 ng/μl, p = 0.2). For the post-dive mean values of endothelial MP, there was no significant difference between both the dives.

CONCLUSIONS

The Oxygen breathing during decompression has a beneficial effect on bubble formation accelerating the washout of nitrogen loaded in tissues. Secondary oxygen-decompression stop could reduce bubble-induced platelet activation and the pro-coagulant activity of PMP release preventing the thrombotic event in the pathogenesis of decompression sickness.

Characterisation of soluble murine CD137 and its association with systemic lupus

CD137 is a member of the tumor necrosis factor receptor family, and is involved in the regulation of activation, proliferation, differentiation and apoptosis of T cells, B cells, monocytes, dendritic cells, natural killer cells and granulocytes. Here report that soluble forms of murine CD137 (sCD137) are generated by differential splicing and are released by activated T cells. Levels of sCD137 correlate with cell activation and the extent of cell death but not with cellular proliferation. While CD8+ T cells express significantly more cell surface CD137 than CD4+ T cells, both T cell subsets express similar levels of sCD137, resulting a twofold increased ratio of soluble to cell surface CD137 for CD4+ T cells. sCD137 exists as a trimer and a higher order multimer, can bind to CD137 ligand, and inhibits secretion of IL-10 and IL-12. sCD137 is present in sera of mice with autoimmune disease but is undetectable in sera of healthy mice.

Peptide-specific CD8 T regulatory cells use IFN-gamma to elaborate TGF-beta-based suppression

We identified a murine peptide-specific CD8 T regulatory cell population able to suppress responding CD4 T cells. Immunization with OVA, poly(I:C), and anti-4-1BB generated a population of SIINFEKL-specific CD8 T regulatory cells that profoundly inhibited peptide-responding CD4 T cells from cellular division. The mechanism of suppression required IFN-gamma, but IFN-gamma alone was not sufficient to suppress the responding CD4 T cells. The data show that CD8 T regulatory cells were unable to suppress unless they engaged IFN-gamma. Furthermore, even in the absence of recall with peptide, the CD8 T regulatory cells suppressed CD4 responses as long as IFN-gamma was present. To examine the effector mechanism of suppression, we showed that neutralizing TGF-beta inhibited suppression because inclusion of anti-TGF-beta rescued the proliferative capacity of the responding cells. TGF-beta-based suppression was dependent completely upon the CD8 T regulatory cells being capable of binding IFN-gamma. This was the case, although peptide recall of primed IFN-gamma (-/-) or IFN-gammaR(-/-) CD8 T cells up-regulated pro-TGF-beta protein as measured by surface latency-associated peptide expression but yet were unable to suppress. Finally, we asked whether the CD8 T regulatory cells were exposed to active TGF-beta in vivo and showed that only wild-type CD8 T regulatory cells expressed the TGF-beta-dependent biomarker CD103, suggesting that latency-associated peptide expression is not always congruent with elaboration of active TGF-beta. These data define a novel mechanism whereby IFN-gamma directly stimulates CD8 T regulatory cells to elaborate TGF-beta-based suppression. Ultimately, this mechanism may permit regulation of pathogenic Th1 responses by CD8 T regulatory cells.

Biological activities of reverse signal transduction through CD137 ligand

CD137 is a member of the tumor necrosis factor receptor family and a potent regulator of T cell activities. Agonists of CD137 have been used widely and successfully to treat cancer in animal models, and recently, it has become evident that CD137 agonists can also be used to treat autoimmune disease. An aspect of the CD137 receptor/ligand system, which has been comparatively little-explored, is its ability of reverse signaling. Just as is CD137, the CD137 ligand is also expressed as a cell membrane protein, and it too can transduce signals into the cells on which it is expressed. This bidirectional signaling capacity allows the CD137 receptor/ligand system to mediate extensive cross-talk between immune cells and between immune and nonimmune cells. This review summarizes the known activities of the CD137 ligand on the different leukocyte subsets and on cancer cells and discusses their influence on the course of immune responses.