2 MATURATION-ASSOCIATED MOUSE ERYTHROCYTE RECEPTORS OF HUMAN B-CELLS .2. ISOLATION AND PARTIAL CHARACTERIZATION OF A B-CELL LECTIN WITH SPECIFICITY OF R1

  • 1 January 1982
    • journal article
    • research article
    • Vol. 47  (2) , 405-413
Abstract
Trypsin treatment of chronic lymphocytic leukemia (CLL) cells which have the capacity to rosette with mouse erythrocytes (M), the BM+ subtype, inhibits their capacity to rosette and releases a substance into the supernatant which agglutinates mouse and rat erythrocytes but not erythrocytes of 5 other species tested. This substance was named immature B-cell lectin (IBL). The specificity of IBL was further demonstrated by fluorescence labeling, absorption and latex rosetting. IBL does not bind to pronase-treated M (pro M), indicating that it has the specificity of R1 as distinct from R2 which binds to a pronase-resistant ligand on M. Other evidence that IBL is associated with B-cell membrane receptors for mouse erythrocytes is as follows: the amount of IBL released into the supernatant correlated with the trypsin sensitivity of M rosetting with different clones of BM+ CLL cells; only small amounts of IBL were released from non-rosetting cells (T cells and mature B cells); binding properties of IBL were inhibited by extract of M but not extract from ox erythrocytes; and high-titer solutions of IBL conferred the capacity to form M rosettes on certain types of non-rosetting B cells. IBL has a dual binding specificity. Its binding to M is inhibited by fetuin and mannan while its binding to B cells is not inhibited by these substances. The relationship of IBL to other membrane lectins including fibronectin is discussed. Preliminary characterization indicates a high MW (at least 300,000 daltons) glycoprotein which has a pronounced tendency to aggregate in solution. The relationship of IBL to stages of human B-cell maturation is discussed.