Adhesion molecules are proteins that facilitate cell-to-cell or cell-to-matrix interactions. Several key adhesion molecules play crucial roles in the agranulocyte adhesion and diapedesis pathway and ensure that agranulocytes can effectively adhere to and migrate through the endothelium, so they can reach the infection or inflammation sites.
For monocytes and macrophages, integrins are prominent adhesion molecules involved in firm adhesion to the endothelial cells lining blood vessels. Integrin receptors on these immune cells, such as VLA-4 and LFA-1, interact with endothelial cell adhesion molecules like VCAM-1 and ICAM-1. This interaction helps monocytes and macrophages firmly adhere to the vessel wall, enabling them to initiate the process of diapedesis.
Lymphocytes, particularly T cells and B cells, utilize different sets of adhesion molecules. Selectins, such as L-selectin, E-selectin, and P-selectin, participate in the initial tethering and rolling steps, allowing lymphocytes to capture onto endothelial cells. Integrins like LFA-1 and VLA-4 are also crucial for lymphocyte firm adhesion. Additionally, chemokine receptors on lymphocytes, such as CXCR4 or CCR7, guide them to the appropriate sites based on chemotactic signals, facilitating their migration.