HUMAN ECALECTIN, A VARIANT OF HUMAN GALECTIN-9, IS A NOVEL EOSINOPHILCHEMOATTRACTANT PRODUCED BY T-LYMPHOCYTES

A 1.6-kilobase pair cDNA was isolated from a human T-cell-derived expr ession library that encodes a novel eosinophil chemoattractant (design ated ecalectin) expressed during allergic and parasitic responses. Bas ed on its deduced amino acid sequence, ecalectin is a 36kDa protein co nsisting of 323 amino acids. Although ecalectin lacks a hydrophobic si gnal peptide, it is secreted from mammalian cells. Ecalectin is not re lated to any known cytokine or chemokine but rather is a variant of hu man galectin-9, a member of the large family of animal lectins that ha ve affinity for P-galactosides. Recombinant ecalectin, expressed in CO S cells and insect cells, exhibited potent eosinophil chemoattractant activity and attracted eosinophils in vitro and in vivo in a dose-depe ndent manner but not neutrophils, lymphocytes, or monocytes. The findi ng that the ecalectin transcript is present in abundance in various ly mphatic tissues and that its expression increases substantially in ant igen-activated peripheral blood mononuclear cells suggests that ecalec tin is an important T-cell-derived regulator of eosinophil recruitment in tissues during inflammatory reactions. We believe that this is the first report of the expression of an immunoregulatory galectin expres sed by a T-cell line that is selective for eosinophils.