PE-Cy5.5-conjugated anti-mouse primary antibodies are immunoreagents labeled with PE-Cy5.5, a far-red-emitting tandem fluorochrome based on fluorescence resonance energy transfer (FRET). Phycoerythrin (PE) serves as the donor fluorophore and cyanine 5.5 (Cy5.5) as the acceptor. Upon excitation by a 488 nm blue or 561 nm yellow-green laser, PE transfers energy to Cy5.5, which emits at approximately 690–700 nm. These conjugated antibodies enable direct, one-step detection of mouse antigens or immunoglobulins, eliminating the need for secondary reagents and providing a useful far-red detection channel for multicolor panels.

Applications

These reagents are used primarily in flow cytometry for immunophenotyping, rare-event analysis, and multicolor panels alongside FITC, PE, APC, and Pacific Blue. They can also be used in fluorescence microscopy with appropriate filter sets. PE-Cy5.5 is brighter than PerCP-based tandem fluorochromes but less bright than PE alone. It is generally more photostable than PE-Cy7, although aldehyde fixation and permeabilization can degrade the tandem fluorochrome.

Specificity

Specificity is determined by the antibody component. Monoclonal antibodies recognize a single epitope, whereas polyclonal antibodies bind to multiple epitopes. Cross-adsorption helps minimize cross-species reactivity. Notably, PE-Cy5.5 conjugates may bind nonspecifically to cells expressing mouse DEC205, independently of antibody specificity, making appropriate controls essential. Isotype, unstained, and compensation controls are required. Store the reagents protected from light and validate each lot for the intended application.