PD-L1 (also known as Programmed Death Ligand 1, CD274, and B7-H1) is one of two cell surface ligands that engage the negative regulatory T cell surface receptor PD-1. PD-L1 is a Type I transmembrane protein expressed on the plasma membrane of cells, such as activated macrophages and some tumor cells. Because binding of PD-1 by PD-L1 has a suppressive effect on the immune system, inhibition of the PD-1/PD-L1 pathway is a major strategy of immune-oncology therapies. PD-L1 is upregulated in certain cancers, and blocking PD-1 or PD-L1 can inhibit cancer growth. Primary antibodies are available purified, or with a selection of fluorescent CF® Dyes and other labels. CF® Dyes offer exceptional brightness and photostability. Note: Conjugates of blue fluorescent dyes like CF®405S and CF®405M are not recommended for detecting low abundance targets, because blue dyes have lower fluorescence and can give higher non-specific background than other dye colors.