CLONING FROM PURIFIED HIGH ENDOTHELIAL VENULE CELLS OF HEVIN, A CLOSE RELATIVE OF THE ANTIADHESIVE EXTRACELLULAR-MATRIX PROTEIN SPARC

High endothelial venules (HEV) in lymphoid tissues support high levels of lymphocyte extravasion from the blood. We purified high endothelial cells from human tonsils by immunomagnetic selection with MECA-79 MAb to construct an HEV cDNA library. Differential screening of this library using cDNA probes from HEV (plus) or flat-walled vessel (minus) endothelial cells allowed us to characterize a novel human cDNA expressed to high levels in HEV. The cDNA encodes a secreted acidic calcium-binding glycoprotein of 664 aa residues, designated hevin, exhibiting 62% identify with the antiadhesive extracellular matrix protein SPARC, over a region of 232 aa spanning more than four fifths of the SPARC coding sequence. The primary structure and sequence of hevin are similar to SPARC-like proteins from rat and quail, called SC1 or QR1. Hevin could contribute to the induction or maintenance of features of the HEV endothelium that facilitate lymphocyte migration.