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 Alexa Fluor 555
Alexa Fluor™ 555 (AF555, Alexa 555) has an excitation peak at 555 nm and an emission peak at 565 nm, and is spectrally similar to Cy®3 (GE Healthcare), TRITC, iFluor® 555 (ATT Bioquest) and iFluor® 560 (ATT Bioquest). Many flow cytometers are equipped with 532nm lasers, so while Alexa 555 can be used for flow cytometry, PE is more commonly used due to its brightness and spectral characteristics. This dye is commonly used for fluorescence microscopy applications.