About HLA DRB1
HLA-DRB1 belongs to the HLA class II beta chain paralogs. The class II molecule is a heterodimer consisting of an alpha (DRA) and a beta chain (DRB), both anchored in the membrane. It plays a central role in the immune system by presenting peptides derived from extracellular proteins. Class II molecules are expressed in antigen presenting cells. The beta chain is approximately 26-28 kDa. It is encoded by 6 exons. Exon one encodes the leader peptide; exons 2 and 3 encode the two extracellular domains; exon 4 encodes the transmembrane domain; and exon 5 encodes the cytoplasmic tail. Within the DR molecule the beta chain contains all the polymorphisms specifying the peptide binding specificities. Hundreds of DRB1 alleles have been described and some alleles have increased frequencies associated with certain diseases or conditions. For example, DRB1*1302 has been related to acute and chronic hepatitis B virus persistence. There are multiple pseudogenes of this gene. [provided by RefSeq, Jul 2020]

About Alexa Fluor 647
Alexa Fluor™ 647 (AF647, Alexa 647) has an excitation peak at 650 nm and an emission peak at 665 nm, and is spectrally similar to Cy®5 (GE Healthcare), iFluor® 647 (ATT Bioquest), and DyLight™ 650 (Thermo Fisher Scientific). Alexa 647 is commonly used for flow cytometry, microscopy, super-resolution microscopy applications. It is very bright, photostable, and pH insensitive, all of which contribute to sensitive detection while using this dye.