| Summary: | <p>Abstract</p> <p>Genes in the Leukocyte Antigen 6 (<it>Ly-6</it>) superfamily encode glycosyl-phosphatidylinositol (GPI) anchored glycoproteins (gp) with conserved domains of 70 to 100 amino acids and 8 to 10 cysteine residues. Murine <it>Ly-6 </it>genes encode important lymphocyte and hematopoietic stem cell antigens. Recently, a new member of the human <it>Ly-6 </it>gene superfamily has been described, <it>CD177</it>. <it>CD177 </it>is polymorphic and has at least two alleles, <it>PRV-1 </it>and <it>NB1</it>. <it>CD177 </it>was first described as <it>PRV-1</it>, a gene that is overexpressed in neutrophils from approximately 95% of patients with polycythemia vera and from about half of patients with essential thrombocythemia. <it>CD177 </it>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 <it>CD177 </it>allele they described <it>NB1</it>. 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 <it>CD177 </it>in the pathogenesis and clinical course of polycythemia vera and essential thrombocythemia are not yet known. However, measuring neutrophil <it>CD177 </it>mRNA levels has become an important marker for diagnosing the myeloproliferative disorders polycythemia vera and essential thrombocythemia.</p>
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