PD-1 PD-L1 Pathway Diagram
An interactive map of the PD-1/PD-L1 axis: the tumour–T-cell synapse sits at the top and the intracellular signalling cascades downward to the nucleus. Nodes are colour-coded by protein class (see Legend). Hover any molecule for detail; click any protein to open the matching Assay Genie product — surface targets link to In Vivo functional-grade antibodies, intracellular signalling proteins to ELISA kits.
The programmed death-1 (PD-1 / CD279) receptor is an inhibitory immune checkpoint expressed on activated T cells. Its ligands PD-L1 (B7-H1 / CD274) and PD-L2 (CD273) are displayed by tumour cells and antigen-presenting cells. Productive T-cell activation normally requires two signals: antigen recognition through the TCR/CD3 complex (Signal 1) and co-stimulation through CD28 engaging CD80/CD86 (Signal 2). These converge on the proximal kinases LCK and ZAP-70 and the adaptor LAT, driving three effector arms — PLCγ1→PKCθ→NF-κB, RAS→RAF→MEK→ERK→AP-1, and PI3K→AKT→mTOR with Ca2+/Calcineurin→NFAT — that together license proliferation, IL-2/IFN-γ production, survival and cytotoxicity.
When PD-1 engages PD-L1 or PD-L2, its cytoplasmic ITIM/ITSM motifs are phosphorylated and recruit the phosphatase SHP-2 (PTPN11). SHP-2 dephosphorylates CD28, ZAP-70 and PI3K signalling nodes — the molecular "brake" that damps AKT and RAS/ERK output. Sustained signalling drives T-cell exhaustion: reduced proliferation, cytokine secretion and tumour killing. CTLA-4 reinforces inhibition by out-competing CD28 for CD80/86 and recruiting PP2A, while LAG-3 and TIM-3 act as additional co-inhibitory checkpoints.
Checkpoint blockade with anti-PD-1 or anti-PD-L1 antibodies interrupts the PD-1–PD-L1 interaction, releasing the SHP-2 brake and restoring anti-tumour T-cell activity — the basis of checkpoint-immunotherapy research. Assay Genie In Vivo functional-grade (low / ultra-low endotoxin) antibodies against PD-1, PD-L1, PD-L2, CTLA-4, CD28, LAG-3 and TIM-3 are designed for these in vivo blocking studies. For research use only; not for diagnostic or therapeutic procedures. Mouse targets shown.
Every protein node links to a product: surface checkpoints open Assay Genie In Vivo functional-grade antibodies, and intracellular signalling proteins open the matching ELISA kit.