SIRP Family of Immune Checkpoint Proteins

SIRPs are paired receptors, with similar extracellular domains but different transmembrane and cytoplasmic regions which result in opposing signals, either activating or inhibitory. The best studied SIRP family member is SIRP alpha. SIRP alpha expression is restricted to myeloid cells while its binding partner CD47 is expressed on T cells. Reagents blocking the SIRP-alpha/CD47 interaction could activate macrophages or dendritic cells to stimulate phagocytosis and to eliminate tumor cells. Preclinical studies have suggested that SIRP alpha or CD47 blockade may have synergistic antitumor effects in combination with other immune checkpoint inhibitors that target the adaptive immune system. SIRP gamma also binds to CD47, albeit with lower affinity than SIRP alpha. While a SIRP beta ligand remains unknown, SIRP beta has been shown to associate with the adaptor protein DAP12 via a basic amino acid motif in its cytoplasmic region leading to activation phagocytosis by macrophages.

SIRP alpha bioactivity QC testing

Human SIRP alpha Support the Adhesion of Red Blood Cells. Red blood cells from human whole blood were incubated with the indicated concentrations of immobilized Recombinant Human SIRPα/CD172a Fc (Catalog # 4546-SA) and red blood cell adhesion was assessed. The ED50 for this effect is 0.6-2.4 μg/mL.

Recombinant Human SIRP alpha Binds the Receptor CD47 in an ELISA Binding Assay. When Recombinant Human SIRP alpha /CD172a His-tag (Catalog # 9378-SA) is coated at 0.5 μg/mL, 100 μL/well, Recombinant Human CD47 Fc Chimera (Catalog # 4670-CD) binds with an ED50 of 0.04-0.24 μg/mL.

Supports the Adhesion of Red Blood Cells. Mouse red blood cells were incubated with the indicated concentrations of Mouse SIRP alpha Fc (Catalog # 7154-SA) and red blood cell adhesion was assessed. The ED50 for this effect is 0.4-1.6 μg/mL.

View other Immune-checkpoint blockade targets

• Butyrophilins
• AMIGOs
• LILRA/B Receptors
• B7/CD28 Family
• CEACAM
• VSIG
• VSTM

Related Pathways

T Cell Co-Signaling Pathway: Ligand-Receptor Interactions

Mechanisms of Regulatory T Cell-Mediated Suppression

Other immune-checkpoint blockade resources:

• Current and Emerging Immune Checkpoint Targets for Immuno-Oncology Research eBook
• Immune Checkpoint
• Immune Checkpoint Blockade: Immune Checkpoint Molecule Expression
• Immune Checkpoint Blockade: Immune Cell Phenotyping and Isolation
• VSIG8 Poster: Co-inhibitory Immune Checkpoint Molecule
• Webinar Short: B7-related Butryophilins as Immune Modulators
• Immunotherapy
• A Role for VSIG-3/VISTA Signaling in Acquired Resistance to Anti-PD-1 Therapy?

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