AffinityImmuno Products

Introduction

PD-L2, encoded by the PDCD1LG2 gene, is a roughly 31 kDa transmembrane immunoglobulin-family protein built from an Ig-like V-type domain and a C2-type domain anchored by a short cytoplasmic tail. Alongside PD-L1, it serves as one of two known ligands for the checkpoint receptor PD-1 on T cells, and its engagement dampens T-cell proliferation, cytokine output, cytolytic activity, and cell survival, pushing chronically stimulated T cells toward an exhausted state. Through this mechanism PD-L2 contributes to maintaining tolerance toward self-antigens and has been implicated in immune privilege during pregnancy, graft acceptance, autoimmune conditions, and tumor immune evasion, while elevated expression has also been reported as a marker in pulmonary tuberculosis. Because a soluble form circulates in blood, sensitive sandwich immunoassays have been developed to quantify PD-L2 as a companion readout alongside PD-1 and PD-L1 in immune-monitoring studies.

Because a soluble form of PD-L2 circulates independently of the cell surface, this assay is used alongside PD-1/PD-L1 immunoassays in immune-checkpoint combination studies, and elevated PD-L2 has separately been explored as a biomarker in active pulmonary tuberculosis.

Principle of the Assay

This kit uses a sandwich enzyme immunoassay format in which the microtiter plate wells are pre-coated with a capture antibody specific to human PD-L2 (PDCD1LG2). Standards or samples are pipetted into the appropriate wells together with a biotin-conjugated detection antibody that also recognizes human PD-L2. Avidin conjugated to horseradish peroxidase (HRP) is then added to each well and allowed to incubate. Upon addition of TMB substrate solution, a colorimetric signal develops exclusively in wells where human PD-L2, the biotin-conjugated detection antibody, and the avidin-HRP conjugate are all present. The enzymatic reaction is stopped by the addition of a sulphuric acid stop solution, and absorbance is measured spectrophotometrically at 450 nm (± 10 nm). Sample concentrations are derived by interpolating the measured optical densities against a standard curve.