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Soluble CD276 (B7-H3) is released from monocytes, dendritic cells and activated T cells and is detectable in normal
Guangbo Zhang1, Jianquan Hou, Jinfang Shi
1Clinical Immunology Laboratory, Suzhou University no. 1 Affiliated Hospital, Suzhou, China.
Insights
Researchers discovered a soluble form of B7-H3 (sB7-H3) released by immune cells and carcinoma cells. This soluble B7-H3 is functionally active and present at high levels in human serum, suggesting a role in regulating immune responses.
Area of Science:
- Immunology
- Molecular Biology
- Cancer Biology
Background:
- Membrane CD276 (mB7-H3) is expressed on immune cells and carcinoma cells, but its in vivo function is unclear.
- The existence and function of a soluble form of B7-H3 (sB7-H3) have not been previously investigated.
Purpose of the Study:
- To investigate the presence and release of soluble B7-H3 (sB7-H3).
- To characterize the functional activity of sB7-H3 in vitro and in vivo.
- To explore the mechanism of sB7-H3 release.
Main Methods:
- Developed a sensitive dual monoclonal antibody sandwich enzyme-linked immunosorbent assay (ELISA) to detect sB7-H3.
- Utilized Western blotting to determine the molecular size of sB7-H3.
- Investigated the effect of matrix metalloproteinase inhibitors (MMPI) on sB7-H3 release.
- Analyzed serum samples from over 200 individuals to quantify circulating sB7-H3 levels.
- Assessed the binding of sB7-H3 to the B7-H3 receptor (B7-H3R) on activated T cells.
Main Results:
- Demonstrated the release of sB7-H3 by monocytes, dendritic cells (DCs), activated T cells, and mB7-H3+ carcinoma cells.
- Showed that sB7-H3 release is mediated by matrix metalloproteinases (MMPs) and can be blocked by MMPI.
- Confirmed high levels of circulating sB7-H3 in all analyzed serum samples.
- Determined the molecular size of sB7-H3 to be approximately 16 kDa via Western blotting.
- Confirmed that sB7-H3 is functionally active by demonstrating its binding to B7-H3R on activated T cells.
Conclusions:
- Soluble B7-H3 (sB7-H3) is actively released from cells, likely via MMP-mediated cleavage.
- Circulating sB7-H3 is abundant and functionally active, suggesting a significant role in regulating B7-H3R/B7-H3 interactions in vivo.
- The cleavage of membrane-bound B7-H3 to a soluble form may modulate both proximal and distal cellular responses, impacting immune regulation and potentially cancer progression.
Abstract:
Expression of membrane CD276 (mB7-H3) has been reported on dendritic cells (DCs), monocytes, activated T cells, and various carcinoma cells. However, reports concerning its in vivo function have been inconsistent. Moreover, whether there is a soluble form of this protein is not known. In this study, using a sensitive dual monoclonal antibody sandwich enzyme-linked immunosorbent assay (ELISA) to detect the soluble form of B7-H3 (sB7-H3), we demonstrated the release of sB7-H3 by monocytes, DCs, activated T cells, and various mB7-H3+ but not mB7-H3- carcinoma cells. Release from cells was blocked by addition of a matrix metalloproteinase inhibitor (MMPI), which concomitantly caused the accumulation of B7-H3 on the cell surface. To determine the level of circulating sB7-H3, more than 200 serum samples were included in the study. The results indicated that sB7-H3 was present at high levels in all serum samples. Western blotting of sB7-H3 from cell culture supernatants or sera of healthy donors indicated that the molecular size was approximately 16 kDa. Soluble B7-H3 was able to bind to the B7-H3 receptor (B7-H3R) on activated T cells, which showed that sB7-H3 is a functionally active form. These results indicate that release of sB7-H3 from the cell surface is mediated by a matrix metalloproteinase and probably regulates B7-H3R/B7-H3 interactions in vivo. Cleavage of sB7-H3 to an active soluble form would alter both proximal and distal cellular responses.
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