Macrophage phagocytosis cd47 sirpa pathway
Whether a macrophage eats a cell is decided by the balance of “eat-me” and “don’t-eat-me” signals it reads on that cell’s surface. Opsonising IgG engages the activating Fcγ receptors FcγRI (CD64), FcγRIII (CD16) and mouse FcγRIV (CD16-2), while complement C1q and C3b/iC3b engage CR3 (CD11b/CD18) and CR4 (CD11c/CD18). Apoptotic cells expose phosphatidylserine, which is read directly by TIM-4, CD36 and Stabilin/BAI1-type receptors and indirectly through the bridging molecules Gas6, Protein S and MFG-E8 feeding the TAM kinases MerTK/Axl/Tyro3 and αvβ5; surface calreticulin partnered with LRP1 (CD91) is the pro-phagocytic counterweight. Activating receptors signal through the ITAM adaptor FcRγ to Lyn, Syk, Btk, PLCγ2 and PI3Kδ, then to Rac1, Cdc42, WASP and Arp2/3 to build the actin cup, with RhoA–ROCK1–myosin-IIA closing it. Against this, CD47 ligating SIRPα (CD172a), CD24 ligating Siglec-10/G, PD-L1 ligating PD-1, MHC-I ligating LILRB1 and FcγRIIB all recruit the ITIM phosphatases SHP-1, SHP-2 and SHIP1 to abort the cup — the checkpoint that anti-CD47 and anti-SIRPα antibodies release to unlock antibody-dependent cellular phagocytosis (ADCP). Internalised cargo then matures through Rab5–EEA1 to Rab7–LAMP1–cathepsin D, is oxidised by NOX2/p47phox, and in LC3-associated phagocytosis is decorated with LC3B under Rubicon control — setting a tolerogenic IL-10/TGF-β or an inflammatory TNF/IL-1β output. Click any protein for the matching Assay Genie In Vivo antibody or ELISA kit.
Recognition — opsonic and apoptotic-cell arms. Antibody-coated targets present clustered Fc domains to FcγRI (CD64), FcγRIII (CD16) and, in mouse, the high-affinity IgG2a receptor FcγRIV (CD16-2); all three signal through the ITAM-bearing common FcRγ (FCER1G) chain, whereas FcγRIIB carries an ITIM and sets the activating-to-inhibitory ratio that predicts ADCP efficacy. Complement-opsonised targets are read by CR3 (CD11b/CD18, Mac-1) and CR4 (CD11c/CD18) after C1q initiates the cascade and C3b is processed to iC3b, with C5aR1 (CD88) priming the response. Dying cells take a separate route: loss of flippase activity exposes phosphatidylserine, engaged directly by TIM-4, CD36 and scavenger receptors (MSR1, TREM2, CD206, Dectin-1 for fungal cargo), and indirectly through the γ-carboxylated bridging ligands Gas6 and Protein S onto the TAM receptor kinases MerTK, Axl and Tyro3, and through MFG-E8 onto αvβ5. Surface calreticulin read by LRP1 (CD91) is the dominant pro-phagocytic “eat-me” determinant on stressed tumour cells.
The ITAM arm builds the cup; the ITIM arm dissolves it. Receptor clustering lets Lyn phosphorylate FcRγ ITAMs, recruiting Syk, which activates Btk, PLCγ2 and PI3Kδ. The resulting PIP3 recruits Akt and the GEFs Vav1 and, on the efferocytic side, the CrkII–DOCK180–ELMO1 module. Rac1 and Cdc42 then drive WASP and the Arp2/3 complex to nucleate the branched F-actin phagocytic cup, while RhoA–ROCK1–myosin-IIA supplies the contractile force that seals it. Every “don’t-eat-me” receptor converges on the same brake: CD47 ligating SIRPα (CD172a), CD24 ligating Siglec-10 / Siglec-G, PD-L1 ligating PD-1, MHC-I (β2M) ligating LILRB1, CD200 ligating CD200R and FcγRIIB itself all recruit SHP-1 (PTPN6) and SHP-2 (PTPN11) to dephosphorylate Syk and myosin-IIA, and SHIP1 (INPP5D) plus PTEN to degrade PIP3, with Csk holding the Src-family kinases inactive. Blocking any one arm of this checkpoint lowers the threshold for engulfment; blocking CD47 or SIRPα together with an opsonising antibody is the combination that has driven the ADCP field.
Phagosome maturation, LAP and the In Vivo opportunity. The sealed phagosome acquires Rab5 and EEA1, converts to a Rab7-positive late phagosome, then fuses with lysosomes to gain LAMP1 and the acid protease cathepsin D. NOX2 (CYBB) with its cytosolic subunit p47phox (NCF1) assembles on the membrane to deliver a reactive-oxygen burst, and in LC3-associated phagocytosis Rubicon stabilises the NOX2-containing complex so that LC3B is conjugated directly onto the single-membrane phagosome — a route that biases towards tolerogenic IL-10 and TGF-β output, whereas canonical inflammatory engulfment yields TNF and IL-1β and cross-presentation of cargo peptides on MHC-I. Because the decisive nodes are surface receptors, this map is unusually well covered by the Assay Genie In Vivo low-endotoxin range: anti-CD47 (MIAP410), anti-SIRPα/CD172a, anti-CD24, anti-PD-L1, anti-PD-1, anti-MHC-I, anti-CD200, anti-CD16/CD32 (2.4G2), anti-FcγRIV (9E9), anti-CD11b, anti-CD11c, anti-CD18, anti-CSF1R (CD115), anti-F4/80 and matched IgG2a isotype controls all perturb this map in vivo, while ELISA kits quantify every intracellular node and secreted output. For research use only; not for diagnostic or therapeutic procedures.
Every protein node links to a product — In Vivo antibody, ELISA kit or research antibody.