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Costimulation of T cell activation by integrin-associated protein (CD47) is an adhesion-dependent, CD28-independent signaling pathway.

Reinhold MI, Lindberg FP, Kersh GJ, Allen PM, Brown EJ - J. Exp. Med. (1997)

Bottom Line: Here, we show that mAbs recognizing IAP can enhance proliferation of primary human T cells in the presence of low levels of anti-CD3, but have no effect on T cell proliferation on their own.IAP costimulation does not require CD28.We hypothesize that anti-IAP generates the costimulatory signal because it modulates interactions of the IgV domain with other plasma membrane molecules; this in turn activates effector functions of the multiply membrane-spanning domain of IAP.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA.

ABSTRACT
The integrin-associated protein (IAP, CD47) is a 50-kD plasma membrane protein with a single extracellular immunoglobulin variable (IgV)-like domain, a multiply membrane-spanning segment, and alternatively spliced short cytoplasmic tails. On neutrophils, IAP has been shown to function in a signaling complex with beta 3 integrins. However, the function of IAP on T cells, which express little or no beta 3 integrin, is not yet defined. Here, we show that mAbs recognizing IAP can enhance proliferation of primary human T cells in the presence of low levels of anti-CD3, but have no effect on T cell proliferation on their own. Together with suboptimal concentrations of anti-CD3, engagement of IAP also enhances IL-2 production in Jurkat cells, an apparently integrin-independent function of IAP. Nonetheless, costimulation by IAP ligation requires cell adhesion. IAP costimulation does not require CD28. Furthermore, anti-IAP, but not anti-CD28, synergizes with suboptimal anti-CD3 to enhance tyrosine phosphorylation of the CD3 zeta chain and the T cell-specific tyrosine kinase Zap70. Ligation of human IAP transfected into the hemoglobin-specific 3.L2 murine T cell hybridoma costimulates activation for IL-2 secretion both with anti-CD3 and with antigenic peptides on antigen-presenting cells (APCs). Moreover, ligation of IAP but not CD28 can convert antagonist peptides into agonists in 3.L2 cells. Using costimulation by IAP ligation as an assay to analyze the structure-function relationships in IAP signaling, we find that both the extracellular and multiply membrane-spanning domains of IAP are necessary for synergy with the antigen receptor, but the alternatively spliced cytoplasmic tails are not. These data demonstrate that IAP ligation initiates an adhesion-dependent costimulatory pathway distinct from CD28. We hypothesize that anti-IAP generates the costimulatory signal because it modulates interactions of the IgV domain with other plasma membrane molecules; this in turn activates effector functions of the multiply membrane-spanning domain of IAP. This model may have general significance for how IAP functions in cell activation.

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IAP can convert antagonist peptides I72 and A72 to agonists.  3.L2 clones transfected with hIAP form 2 (closed symbol) or IAP/CD7  (open symbol) were activated with the indicated concentration of the  Hb(64–76)–I72 (A) or Hb(64–76)–A72 (B) peptide presented by CH27  cells in the presence of anti-IAP mAbs 2E11, 2D3 or B6H12, anti CD28  (37.51), or a control mAb (IB4). I72 and A72 have been shown previously to have significant antagonist but no activating effects on 3.L2 (30).  T cell activation was measured as described in Fig. 2 B. The values shown  represent averages of triplicates of 1 experiment of >3 with similar results.
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Figure 6: IAP can convert antagonist peptides I72 and A72 to agonists. 3.L2 clones transfected with hIAP form 2 (closed symbol) or IAP/CD7 (open symbol) were activated with the indicated concentration of the Hb(64–76)–I72 (A) or Hb(64–76)–A72 (B) peptide presented by CH27 cells in the presence of anti-IAP mAbs 2E11, 2D3 or B6H12, anti CD28 (37.51), or a control mAb (IB4). I72 and A72 have been shown previously to have significant antagonist but no activating effects on 3.L2 (30). T cell activation was measured as described in Fig. 2 B. The values shown represent averages of triplicates of 1 experiment of >3 with similar results.

Mentions: To test whether the nature of the peptide ligand affected the ability of IAP to costimulate T cell activation, the effects of APL peptides on 3.L2 activation were tested. The two antagonist peptides chosen were previously shown to have no agonist effects on 3.L2 (30), because they did not induce any IL-2 production from 3.L2 cells on their own even at concentrations above 100 μM. When tested in combination with anti-IAP, both peptides induced the T cell hybridoma to make IL-2 (Fig. 6). In contrast, addition of anti-CD28 mAb did not result in IL-2 production by the 3.L2 clones. Thus, coligation of IAP but not CD28 with the antigen receptor gives a fully activating signal, even with peptides incapable of producing any activating signal on their own.


Costimulation of T cell activation by integrin-associated protein (CD47) is an adhesion-dependent, CD28-independent signaling pathway.

Reinhold MI, Lindberg FP, Kersh GJ, Allen PM, Brown EJ - J. Exp. Med. (1997)

IAP can convert antagonist peptides I72 and A72 to agonists.  3.L2 clones transfected with hIAP form 2 (closed symbol) or IAP/CD7  (open symbol) were activated with the indicated concentration of the  Hb(64–76)–I72 (A) or Hb(64–76)–A72 (B) peptide presented by CH27  cells in the presence of anti-IAP mAbs 2E11, 2D3 or B6H12, anti CD28  (37.51), or a control mAb (IB4). I72 and A72 have been shown previously to have significant antagonist but no activating effects on 3.L2 (30).  T cell activation was measured as described in Fig. 2 B. The values shown  represent averages of triplicates of 1 experiment of >3 with similar results.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2211576&req=5

Figure 6: IAP can convert antagonist peptides I72 and A72 to agonists. 3.L2 clones transfected with hIAP form 2 (closed symbol) or IAP/CD7 (open symbol) were activated with the indicated concentration of the Hb(64–76)–I72 (A) or Hb(64–76)–A72 (B) peptide presented by CH27 cells in the presence of anti-IAP mAbs 2E11, 2D3 or B6H12, anti CD28 (37.51), or a control mAb (IB4). I72 and A72 have been shown previously to have significant antagonist but no activating effects on 3.L2 (30). T cell activation was measured as described in Fig. 2 B. The values shown represent averages of triplicates of 1 experiment of >3 with similar results.
Mentions: To test whether the nature of the peptide ligand affected the ability of IAP to costimulate T cell activation, the effects of APL peptides on 3.L2 activation were tested. The two antagonist peptides chosen were previously shown to have no agonist effects on 3.L2 (30), because they did not induce any IL-2 production from 3.L2 cells on their own even at concentrations above 100 μM. When tested in combination with anti-IAP, both peptides induced the T cell hybridoma to make IL-2 (Fig. 6). In contrast, addition of anti-CD28 mAb did not result in IL-2 production by the 3.L2 clones. Thus, coligation of IAP but not CD28 with the antigen receptor gives a fully activating signal, even with peptides incapable of producing any activating signal on their own.

Bottom Line: Here, we show that mAbs recognizing IAP can enhance proliferation of primary human T cells in the presence of low levels of anti-CD3, but have no effect on T cell proliferation on their own.IAP costimulation does not require CD28.We hypothesize that anti-IAP generates the costimulatory signal because it modulates interactions of the IgV domain with other plasma membrane molecules; this in turn activates effector functions of the multiply membrane-spanning domain of IAP.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA.

ABSTRACT
The integrin-associated protein (IAP, CD47) is a 50-kD plasma membrane protein with a single extracellular immunoglobulin variable (IgV)-like domain, a multiply membrane-spanning segment, and alternatively spliced short cytoplasmic tails. On neutrophils, IAP has been shown to function in a signaling complex with beta 3 integrins. However, the function of IAP on T cells, which express little or no beta 3 integrin, is not yet defined. Here, we show that mAbs recognizing IAP can enhance proliferation of primary human T cells in the presence of low levels of anti-CD3, but have no effect on T cell proliferation on their own. Together with suboptimal concentrations of anti-CD3, engagement of IAP also enhances IL-2 production in Jurkat cells, an apparently integrin-independent function of IAP. Nonetheless, costimulation by IAP ligation requires cell adhesion. IAP costimulation does not require CD28. Furthermore, anti-IAP, but not anti-CD28, synergizes with suboptimal anti-CD3 to enhance tyrosine phosphorylation of the CD3 zeta chain and the T cell-specific tyrosine kinase Zap70. Ligation of human IAP transfected into the hemoglobin-specific 3.L2 murine T cell hybridoma costimulates activation for IL-2 secretion both with anti-CD3 and with antigenic peptides on antigen-presenting cells (APCs). Moreover, ligation of IAP but not CD28 can convert antagonist peptides into agonists in 3.L2 cells. Using costimulation by IAP ligation as an assay to analyze the structure-function relationships in IAP signaling, we find that both the extracellular and multiply membrane-spanning domains of IAP are necessary for synergy with the antigen receptor, but the alternatively spliced cytoplasmic tails are not. These data demonstrate that IAP ligation initiates an adhesion-dependent costimulatory pathway distinct from CD28. We hypothesize that anti-IAP generates the costimulatory signal because it modulates interactions of the IgV domain with other plasma membrane molecules; this in turn activates effector functions of the multiply membrane-spanning domain of IAP. This model may have general significance for how IAP functions in cell activation.

Show MeSH
Related in: MedlinePlus