About CD4
This gene encodes the CD4 membrane glycoprotein of T lymphocytes. The CD4 antigen acts as a coreceptor with the T-cell receptor on the T lymphocyte to recognize antigens displayed by an antigen presenting cell in the context of class II MHC molecules. The CD4 antigen is also a primary receptor for entry of the human immunodeficiency virus through interactions with the HIV Env gp120 subunit. This gene is expressed not only in T lymphocytes, but also in B cells, macrophages, granulocytes, as well as in various regions of the brain. The protein functions to initiate or augment the early phase of T-cell activation, and may function as an important mediator of indirect neuronal damage in infectious and immune-mediated diseases of the central nervous system. Multiple alternatively spliced transcript variants encoding different isoforms have been identified in this gene. [provided by RefSeq, May 2020]

About Alexa Fluor 680
Alexa Fluor™ 680 (AF680, Alexa 680) has an excitation peak at 679 nm and an emission peak at 702 nm, and is spectrally similar to Cy®5.5 (GE Healthcare), IR680® (Licor), iFluor® 680 (ATT Bioquest) and iFluor® 700 (ATT Bioquest). Alexa 680 is commonly used for flow cytometry, fluorescence microscopy and super-resolution microscopy.