The recombinant human BTLA protein used in affinity tests was purchased form Novoprotein (Company product code: C563). For ELISA, recombinant human BTLA-Fc, HVEM-Fc as well as anti-human BTLA (#7.1) blocking monoclonal antibody (mAb) and anti-human HVEM (#11.8) non-blocking mAb were described previously . Anti-HVEM mAb was biotinylated using the Biotin Labeling Kit-NH2 (Abnova, #KA0003), according manufacturer’s instruction.