Km. Mcnagny et al., THE EOSINOPHIL-SPECIFIC CELL-SURFACE ANTIGEN, EOS47, IS A CHICKEN HOMOLOG OF THE ONCOFETAL ANTIGEN MELANOTRANSFERRIN, Blood, 87(4), 1996, pp. 1343-1352
The EOS47 antigen is a 100-kD cell surface glycoprotein selectively ex
pressed by avian retrovirus-transformed eosinophils and their precurso
rs. We have purified the EOS47 protein to homogeneity and used peptide
sequence information to clone EOS47-encoding cDNAs. The open reading
frames from these cDNAs predict a 738 amino acid protein with homology
to human melanotransferrin, a membrane-bound, transferrin-like protei
n that is expressed at high levels by a subset of melanomas, tumor cel
l lines, fetal intestine, and liver, but not by most normal adult tiss
ues. The predicted protein sequence of EOS47 displays a 61% sequence i
dentity with melanotransferrin and conservation of all 28 cysteine res
idues, indicating a similar tertiary structure. The finding that EOS47
lacks several of the iron-coordinating amino acids present in all tra
nsferrins suggests that it may be impaired in its ability to bind iron
. In nonhematopoietic tissues, EOS47 is expressed at high levels by ep
ithelial brush borders of small intestine and kidney and at lower leve
ls by cells lining the sinusoids of the liver. Within hematopoietic ti
ssues, EOS47 is restricted to a subpopulation of cells (1% to 5%) in b
one marrow and early spleen and fluorescence-activated cell sorting of
EOS47(+) cells leads to a dramatic (>30-fold) enrichment of peroxidas
e(+) eosinophils. In contrast, peripheral blood eosinophils are EOS47(
-). suggesting that the antigen is expressed by newly formed eosinophi
ls and that expression ceases shortly before these cells emigrate from
the bone marrow into the peripheral blood. Our results show that mela
notransferrin is a stage-specific marker of eosinophils and should be
useful for their isolation and further characterization. (C) 1996 by T
he American Society of Hematology.