CD11b

CD11b, also known as integrin alpha M or ITGAM, is a cell surface molecule that pairs with CD18 to form the integrin αMβ2, commonly referred to as Mac-1 or complement receptor 3 (CR3).

It is primarily expressed on myeloid cells, including neutrophils, monocytes, macrophages, subsets of dendritic cells, and some natural killer cells.

CD11b binds a range of ligands, including iC3b, other opsonins of the complement system, and matrix components. It supports adhesion to endothelium and other cells, often in concert with CD18, and participates in the phagocytosis of opsonized particles.

As part of CR3, CD11b mediates phagocytosis, microbial killing, and inflammatory signaling. It recognizes fungi and bacteria and can promote respiratory burst in phagocytes; it also mediates migration and extravasation of leukocytes to sites of inflammation.

Activation of CD11b involves inside-out signaling from chemokines and other stimuli, inducing conformational changes that increase affinity for ligands; cytoplasmic tails interact with cytoskeletal proteins such as talin, linking adhesion to the actin cytoskeleton.

Clinical relevance: CD11b is important for innate immunity and clearance of pathogens; loss or dysfunction can impair phagocytosis and host defense. Altered CD11b activity has been studied in inflammatory and autoimmune diseases, and has been explored as a therapeutic target to modulate inflammation.

In research contexts, CD11b is used as a marker for myeloid cells and is studied in areas such as cancer immunology and neuroinflammation, where microglia express CD11b and participate in immune surveillance and tissue remodeling.