Fig. 9.7 L-selectin binds to mucinlike vascular addressins. L-selectin is expressed on naive T cells and recognizes carbohydrate motifs. Its binding to sulfated sialyl-LewisX moieties on the vascular addressins Cd34 and GlyCaM-1 on hevs binds the lymphocyte weakly to the endothelium. The relative importance of Cd34 and GlyCaM-1 in this interaction is unclear. Cd34 has a transmembrane anchor and is expressed in appropriately glycosylated form only on hev cells, although it is found in other forms on other endothelial cells. GlyCaM-1 is expressed on hevs but has no transmembrane region and may be secreted into the hevs. The addressin MadCaM-1 is expressed on mucosal endothelium and guides lymphocytes to mucosal lymphoid tissue. The configuration shown represents mouse MadCaM-1, which contains an Iga-like domain closest to the cell membrane; human MadCaM-1 has an elongated mucin-like domain and lacks the Iga-like domain.
Fig. 9.8 Integrins are important in T-lymphocyte adhesion. Integrins are heterodimeric proteins containing a β chain, which defines the class of integrin, and an α chain, which defines the different integrins within a class. The α chain is larger than the β chain and contains binding sites for divalent cations that may be important in signaling. LFa-1 (integrin αL:β2) is expressed on all leukocytes. It binds ICaMs and is important in cell migration and in the interactions of T cells with antigen-presenting cells (apCs) or target cells; it is expressed at higher levels on effector T cells than on naive T cells. Lymphocyte peyer’s patch adhesion molecule (LpaM-1, or integrin α4:β7) is expressed by a subset of naive T cells and contributes to lymphocyte entry into mucosal lymphoid tissues by supporting adhesive interactions with vascular addressin MadCaM-1. vLa-4 (integrin α4:β1) is expressed strongly after T-cell activation. It binds to vCaM-1 on activated endothelium and is important for recruiting effector T cells into sites of infection.
Fig. 9.9 Immunoglobulin superfamily adhesion molecules involved in leukocyte interactions. adhesion molecules of the immunoglobulin superfamily bind to adhesion molecules of various types, including integrins (LFa-1 and vLa-4) and other immunoglobulin superfamily members [the Cd2–Cd58 (LFa-3) interaction]. These interactions have a role in lymphocyte migration, homing, and cell–cell interactions; see Fig. 3.24 for the other molecules listed here.
including LFA-1. This is probably because T cells also express other adhesion molecules, including the immunoglobulin superfamily member CD2 and β1 integrins, which may compensate for the absence of LFA-1. Expression of the β1 integrins increases significantly at a late stage in T-cell activation, and they are thus often called VLAs, for very late activation antigens; they are important in directing effector T cells to inflamed target tissues.