[5] Upon binding with one of a number of alpha chains, CD18 is capable of forming multiple heterodimers, which play significant roles in cellular adhesion and cell surface signaling, as well as important roles in immune responses.

Deficiencies in CD18 expression can lead to adhesion defects in circulating white blood cells in humans, reducing the immune system's ability to fight off foreign invaders.

[5] This is especially important for neutrophils, as cellular adhesion plays a large role in extravasation from the blood vessels.

[9] LFA-1 is involved in adhesion and binding to antigen presenting cells through interactions with the surface protein ICAM-1.

The beta 2 integrins have also been found in a soluble form, meaning they are not anchored into the plasma membrane of the cell, but rather exist outside of the cell in the plasma, and are capable of ligand binding.