CD177: A member of the Ly-6 gene superfamily involved with neutrophil proliferation and polycythemia vera

Genes in the Leukocyte Antigen 6 (Ly-6) superfamily encode glycosyl-phosphatidylinositol (GPI) anchored glycoproteins (gp) with conserved domains of 70 to 100 amino acids and 8 to 10 cysteine residues. Murine Ly-6 genes encode important lymphocyte and hematopoietic stem cell antigens. Recently, a new member of the human Ly-6 gene superfamily has been described, CD177. CD177 is polymorphic and has at least two alleles, PRV-1 and NB1. CD177 was first described as PRV-1, a gene that is overexpressed in neutrophils from approximately 95% of patients with polycythemia vera and from about half of patients with essential thrombocythemia. CD177 encodes NB1 gp, a 58–64 kD GPI gp that is expressed by neutrophils and neutrophil precursors. NB1 gp carries Human Neutrophil Antigen (HNA)-2a. Investigators working to identify the gene encoding NB1 gp called the CD177 allele they described NB1. NB1 gp is unusual in that neutrophils from some healthy people lack the NB1 gp completely and in most people NB1 gp is expressed by a subpopulation of neutrophils. The function of NB1 gp and the role of CD177 in the pathogenesis and clinical course of polycythemia vera and essential thrombocythemia are not yet known. However, measuring neutrophil CD177 mRNA levels has become an important marker for diagnosing the myeloproliferative disorders polycythemia vera and essential thrombocythemia.