What are the molecules involved in margination and diapedesis and what are the steps involved?
The players involved are
: According to Wikipedia, "Integrins are receptors that mediate attachment between a cell and the tissues surrounding it
, which may be other cells or the extracellular matrix (ECM). They also play a role in cell signaling and thereby define cellular shape, mobility, and regulate the cell cycle."
: are transmembrane glycoproteins that play a role in cell adhesion
. They are expressed principally on leukocytes and endothelial cells
, and they can, for example, mark the part of a blood vessel near an infection.
: like selectins, are also present in the endothelial cells near the infection signaling to leukocytes where the site of infection is
- Steps involved for margination & diapedesis:
- 1) Selectins are expressed on endothelial cells around the site of infection.
2) Leukocytes, such as neutrophils, express the ligand for selectins
. The binding of the ligand with the selectin
is weak, however, and cannot hold on for long because of the flow of blood
, so the leukocyte continues to roll along.
, like selectins
, are also present in the endothelial cells near the infection. As the leukocyte is rolling along having weak interactions with selectins
, the chemokine
will eventually bind allowing integrin activation
(from the low-affinity state to the high affinity state).
4) Once the integrin
has been activated, there is stable adhesion between the leukocyte and a receptor.
5) The leukocyte is then able to migrate through the endothelium by margination and diapedesis
to the site of infection.
6) The leukocyte is able to determine where the site of infection is by following the chemokine gradient. Chemokines such as TNF and IL-1 are released from macrophages to signal the site of infection.