BELIMUMAB IS A BLYS-SPECIFIC INHIBITOR THAT BLOCKS THE BINDING OF SOLUBLE BLYS, A B-CELL SURVIVAL FACTOR, TO ITS RECEPTORS ON B CELLS. BELIMUMAB DOES NOT BIND B CELLS DIRECTLY, BUT BY BINDING BLYS, BELIMUMAB INHIBITS THE SURVIVAL OF B CELLS, INCLUDING AUTOREACTIVE B CELLS, AND REDUCES THE DIFFERENTIATION OF B CELLS INTO IMMUNOGLOBULIN-PRODUCING PLASMA CELLS.