Adhesion Molecules in Leukocytes and Their Reactivity - Adhesion Molecules - page 150

Fig. 1 Integrin family of adhesion molecules. h e integrin family of molecules may be divided
according to the extracellular matrix protein or sequence they bind (collagen, laminin, vitronectin,
RGD). β 2 -integrins may be found predominantly on leukocytes, and the most commonly studied
of them are αLβ 2 (LFA-1) and αMβ 2 (Mac-1).

a chain

b chain

Low affinity Intermediate affinity High affinity

Fig. 2 Activation phases of integrin heterodimers. Depending on the activation state of
leukocytes, integrins are present in three dif erent conformational forms. (1) On resting leukocytes,
the closed conformational form of integrins dominates. h e α/β chains are bent down to the cell
membrane forming a genu, knee (low ai nity form). (2) On activated leukocytes, integrins are in
the extended form, where the head of the chains is moved away from the cell membrane while the
α/β chains are tightly at ached to each other (intermediate ai nity form). (3) Further activation
of integrins results in dissociation of the α and β chains followed by external angle of the β -chain.

h is conformational change of β-chain exposes additional binding epitopes (high ai nity form).