About IL-21
This gene encodes a member of the common-gamma chain family of cytokines with immunoregulatory activity. The encoded protein plays a role in both the innate and adaptive immune responses by inducing the differentiation, proliferation and activity of multiple target cells including macrophages, natural killer cells, B cells and cytotoxic T cells. Dysregulation of this gene plays a role in multiple immune-mediated diseases including lupus, psoriasis and chronic inflammatory diseases. Alternatively spliced transcript variants encoding multiple isoforms have been observed for this gene. [provided by RefSeq, Dec 2011]

About PerCP-Cy5.5
PerCP-Cyanine® 5.5 (PerCP-Cy5.5) is a red-emitting tandem fluorophore that was originally designed to make the PerCP fluorophore more stable and increase signal intensity. The donor molecule, PerCP can be excited by the 488-nm blue laser and and transfers energy to the acceptor molecule, Cy5.5, which emitts light that can be captured with a 695/40 nm bandpass filter. PerCP-Cy5.5 has an excitation peak at 482 nm and an emission peak at 695 nm. There are superior alternatives to PerCP and PerCP-Cy5.5 including BB700, NovaFluor Blue 690 or PerCP-eFluor™ 710