Roll, stick and cross
How do immune cells leave the bloodstream to enter infected tissues?
Lymphocytes are a type of cell found in the blood that can detect and fight infections: in particular, some of them can leave the bloodstream to enter infected or inflamed tissues. To do so, these lymphocytes use proteins on their surface to roll along the inside wall of the blood vessel; then they stick to this wall and finally they pass through it. For some types of lymphocytes the details of this mechanism — such as precisely which surface proteins are necessary — remain unclear.
Here, Lee et al. collect human lymphocytes from the blood of healthy donors, and they identify a subgroup of lymphocytes, called MAIT cells, that are particularly good at moving from blood to infected or inflamed tissues, and further experiments reveal the types of surface proteins that help them do so.
Some of these proteins, for example selectin ligands, are important so the MAIT cell can roll on the wall of the blood vessel. Others, like CCR6, are essential for the cell to stop rolling and stick to the wall. Lee et al. also identify C/EBPδ, a regulatory protein inside the MAIT cell that controls how these other two types of proteins are produced. Finally, Lee et al. show that additional proteins, such as CCR2, are necessary for the lymphocyte to cross the vessel wall.
The proteins that help lymphocytes move from blood to tissues represent important targets to fight diseases. For example, blocking these proteins could prevent lymphocytes from invading and damaging healthy tissues, which happens in autoimmune diseases like multiple sclerosis. Alternatively, manipulating these proteins could help to engineer lymphocytes that can invade and kill tumor tissues in cancers.
To find out more
Read the eLife research paper on which this eLife digest is based:
