Allophycocyanin (APC)-conjugated anti-monkey primary antibodies are fluorescent immunoreagents that combine the exceptional brightness of the APC phycobiliprotein with the target specificity of immunoglobulins directed against non-human primate antigens. These reagents are widely employed in flow cytometry, fluorescence-activated cell sorting (FACS), and multicolor immunophenotyping of monkey leukocyte subsets, enabling sensitive detection of cell surface and intracellular markers in preclinical research, vaccine development, and translational medicine. APC is a phycobiliprotein derived from cyanobacteria and red algae and is a potent donor fluorophore for creating tandem dyes that can be excited off the 633–640 nm laser.

The APC Fluorophore

Allophycocyanin (APC) belongs to a family of phycobiliproteins that are well suited as fluorescent reagents for flow cytometric analysis, since they have a broad excitation spectrum, a large Stokes shift, and they fluoresce with a high quantum yield. APC is a fluorescent light-harvesting protein unique to cyanobacteria and red algae. For antibody conjugation, APC is commonly supplied in a cross-linked (XL-APC) and stabilized form, which exhibits a reduced ratio of fluorescence at 650/620 nm versus native APC and is reported to be about 28% more effective in terms of fluorescence quantum yield compared with non-cross-linked APC. The fluorescence quantum yield of crosslinked APC decreases by approximately 20% after labeling on antibody or streptavidin, though the conjugate retains high brightness suitable for detecting antigens with moderate to low expression levels.