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 APC-Fire 810
APC-Fire™ 810 from BioLegend has an excitation peak at 650nm and an emission peak at 807 nm and is spectrally similar to APC-CF®790. APC-Fire™ 810 is most commonly used in flow cytometry. On a 5-laser Cytek® Aurora, it has very limited spectral spillover into any other channel, so it can be assigned to any antigen with moderate to abundant expression and used in combination with any other fluorophore. This dye is very useful for detecting variably expressed markers, like markers of activation, since it emits so far outside of the autofluorescence range.