CD31

CD31 is a cluster of differentiation molecule. It is also called PECAM-1 for platelet endothelial cell adhesion molecule. It plays a key role in removing aged neutrophils from the body. Macrophages palpate any passing neutrophil and have to decide whether the cell is healthy or has to be ingested.

If a neutrophil is dying, it will have phosphatidyl serine in its plasma membrane. Both the neutrophil and the macrophage express CD-31 on their membranes, and during the testing process, these CD-31 molecules bind   the two cells together. If the neutrophil is healthy, it will now fire a signal to the macrophage, and the CD-31 molecules will detach. The neutrophil is now free.

If the neutrophil is not healthy, it will not be able to signal back to the macrophage to prevent its peril. This happens a long time before the neutrophil degrades and releases its dangerous payload to the medium. Macrophages normally release cytokines, when phagocytizing material. When eating a neutrophil, they don't. Neutrophils come of age 6 days after their creation. This signifies a strong turnover rate, one that is even stronger during and after inflammatory processes. It would make no sense to further stimulate the inflammation because of this event. Macrophages ingesting dying neutrophils will, however, release more TGF-Beta, further stimulating tissue repair.

In humans, the gene encoding CD-31 is found on chromosome 17.

CD-31 is normally found on endothelial cells, platelets, macrophages and Kupffer cells, granulocytes, T / NK cells, lymphocytes, megakaryocytes, fibroblasts, osteoclasts, neutrophils.

CD-31 is also expressed in certain tumors, including epithelioid hemangioendothelioma, epithelioid sarcoma-like hemangioendothelioma, other vascular tumors, histiocytic malignancies, and plasmacytomas. It is rarely found in some sarcomas and carcinomas.

In conclusion, CD-31 and macrophages play a key role in tissue regeneration.