Cd47-Signal Regulatory Protein α (Sirpα) Regulates Fcγ and Complement Receptor–Mediated Phagocytosis

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Abstract

In autoimmune hemolytic anemia (AIHA), circulating red blood cells (RBCs) opsonized with autoantibody are recognized by macrophage Fcγ and complement receptors. This triggers phagocytosis and elimination of RBCs from the circulation by splenic macrophages. We recently found that CD47 on unopsonized RBCs binds macrophage signal regulatory protein α (SIRPα), generating a negative signal that prevents phagocytosis of the unopsonized RBCs. We show here that clearance and phagocytosis of opsonized RBCs is also regulated by CD47-SIRPα. The inhibition generated by CD47-SIRPα interaction is strongly attenuated but not absent in mice with only residual activity of the phosphatase Src homology 2 domain–containing protein tyrosine phosphatase (SHP)-1, suggesting that most SIRPα signaling in this system is mediated by SHP-1 phosphatase activity. The macrophage phagocytic response is controlled by an integration of the inhibitory SIRPα signal with prophagocytic signals such as from Fcγ and complement receptor activation. Thus, augmentation of inhibitory CD47-SIRPα signaling may prevent or attenuate RBC clearance in AIHA.

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Most cited references 24

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Phagocytosis by monocytes or neutrophils can be enhanced by interaction with several proteins or synthetic peptides containing the Arg-Gly-Asp sequence. Recently we showed that an mAb, B6H12, specifically inhibited this enhancement of neutrophil phagocytosis by inhibiting Arg-Gly-Asp binding to the leukocyte response integrin (Gresham, H. D., J. L. Goodwin, P. M. Allen, D. C. Anderson, and E. J. Brown. 1989. J. Cell Biol. 108:1935-1943). Now, we have purified the antigen recognized by B6H12 to homogeneity. Surprisingly, it is a 50-kD molecule that is expressed on the plasma membranes of all hematopoietic cells, including erythrocytes, which express no known integrins. On platelets and placenta, but not on erythrocytes, this protein is associated with an integrin that can be recognized by an anti-beta 3 antibody. In addition, both the anti-beta 3 and several mAbs recognizing the 50-kD protein inhibit Arg-Gly-Asp stimulation of phagocytosis. These data demonstrate an association between integrins and the 50-kD protein on several cell types. For this reason, we call it Integrin-associated Protein (IAP). We hypothesize that IAP may play a role in signal transduction for enhanced phagocytosis by Arg-Gly-Asp ligands.

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Mice homozygous for the recessive allelic mutation motheaten (me) or viable motheaten (mev) on chromosome 6 develop severe defects in hematopoiesis. In this paper we present the findings that the me and mev mutations are within the hematopoietic cell protein-tyrosine phosphatase (Hcph) gene. High resolution mapping localized me to an area tightly linked to Hcph on chromosome 6. Abnormalities of the Hcph protein product were demonstrated by Western blot analysis and by activity assays in both me/me and mev/mev mice. Molecular analysis of the Hcph cDNA identified abnormal transcripts in both mutants. DNA sequence analyses of cDNA and genomic clones revealed that both the me and mev mutations are point mutations that result in aberrant splicing of the Hcph transcript. These findings provide the first available animal models for a specific protein-tyrosine phosphatase deficiency, thus facilitating determination of the precise role of this signaling molecule in hematopoiesis.

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Author and article information

Contributors

Dept. of Integrative Medical Biology, Section for Histology and Cell Biology, Umeå University, SE-901 87 Umeå, Sweden.46-90-786-669646-90-786-5974

Journal

Journal ID (nlm-ta): J Exp Med

Title: The Journal of Experimental Medicine

Publisher: The Rockefeller University Press

ISSN (Print): 0022-1007

ISSN (Electronic): 1540-9538

Publication date (Print): 2 April 2001

Volume: 193

Issue: 7

Pages: 855-862

Affiliations

[a ]Division of Infectious Diseases, Department of Internal Medicine and Department of Molecular Microbiology and Pathogenesis, Washington University School of Medicine, St. Louis, Missouri 63110

[b ]Research Service, Albuquerque Veterans Administration Medical Center, Albuquerque, New Mexico 87108

[c ]Department of Molecular Genetics and Microbiology, University of New Mexico, Albuquerque, New Mexico 87131

Article

Publisher ID: 010027

DOI: 10.1084/jem.193.7.855

PMC ID: 2193364

PubMed ID: 11283158

SO-VID: 825af344-6dad-4d7a-82f3-e540557d3f5f

History

Date received : 8 January 2001

Date revision requested : 20 February 2001

Date accepted : 28 February 2001

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