Cell spreading distinguishes the mechanism of augmentation of T cell activation by integrin-associated protein/CD47 and CD28

Author: Ticchioni M.  

Publisher: Oxford University Press

ISSN: 1460-2377

Source: International Immunology, Vol.11, Iss.5, 1999-05, pp. : 707-718

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Abstract

Integrin-associated protein (IAP/CD47) is a 50 kDa transmembrane protein initially defined as a regulator of 3 integrin-mediated functions in neutrophils. IAP also can synergize with the TCR in T cell activation independent of 3 integrins. To analyze the mechanism for IAP synergy with TCR, we expressed in Jurkat cells a chimeric molecule, consisting of the CD16 extracellular domain, the CD7 transmembrane domain and the TCR  chain cytoplasmic tail (CD16-7-), which on its own is unable to induce IL-2 production. Ligation of IAP acted in synergy with TCR to induce IL-2 transcription and synthesis, but failed to synergize with the signal generated by CD16-7-, while CD28 was a potent co-stimulator with both TCR and CD16-7-. The failure of IAP to activate Jurkat together with CD16-7- correlated with a lack of c-Jun N-terminal kinase, but not extracellular-signal-regulated kinase activation. Jurkat adhesion to anti-IAP, but not anti-CD28, induced cell spreading and the same domains of IAP required for augmentation of T cell activation were required to induce cell spreading. IAP synergy with TCR signaling likely results from its ability to stimulate adhesion to a ligand-expressing surface or antigen-presenting cell (APC), rather than from initiation of a novel signaling cascade. We conclude that a major role for ligation of IAP in T cell activation is to enhance the efficiency of TCR signaling by causing T cells to spread on an APC or surface.