The Significance of Elevated Beta 2-Microglobulin (b2-m) in B-CLL: Evidence of in Vitro b2-m Secretion Following Activation of B-CLL Cells.

Abstract 4380

Beta 2-microglobulin (b2-m) is an 11-kDa protein recognized as the light-chain component of the MHC-I molecule. It is produced by nucleated cells membranes and is detectable in the serum and other body fluids. The link between the b2-m/ MHC-1 molecules and membrane structure has been associated with lymphocyte activation. Serum b2-m is elevated in a variety of disorders and has a prognostic value in lymphoprolifera! tive diseases such as multiple myeloma and CLL. High b2-m in CLL, has been found to correlate mainly with the advanced stage of the disease and high lymphocyte count and is routinely used as a bad prognostic factor (Keating, 1995, Montillo, 2005). Previous studies from our Institute have shown significantly higher level of b2-m in CLL/PL and PLL and in cases associated with autoimmune disorders close to levels found in active myeloma (Shvidel, 1996, Duek, 2006). We suggested that b2-m levels are increased during B-cell activation which not necessarily correlates with aggravation of CLL. In an attempt to further evaluate the correlation of bm-2 and B-cells activation we stimulated B-CLL cells in vitro with pokeweed mitogen (PWM) and compared the results with CLL controls after 3 and 7 days of culture. Level of b2-m in supernatants was tested using a microparticle enzyme immunoassay. B-CLL cells from 8 patients (4 in stage Binet A, 3 B and 1 C) were studied. Except for stage A, the serum b2-m was mildly increased. The results showed a significant in vitro secretion of b2-m after three and seven days in supernatants of PWM-activated cells compared to unstimulated controls: mean values after 3 days were: 188 ng/ml (range 96-279) in activated B-cells versus 57ng/ml (25-103) in controls; and after 7 days 599 ng/ml (401-914) versus 164 (67-267) in controls. Interestingly, CD8+ T-cells from a T-large granular leukemia patient stimulated with PHA do not secrete significant amount of b2-m in vitro (156 ng/ml versus 87 at day 7). Our results demonstrate that activation of B-CLL cells in vitro induced a marked secretion of b2-m. Thus, the significance of b2-m in CLL may correlate with degree of activation of B-CLL cells. This hypothesis is supported by the increase of CD38 (an activation marker) in CLL cases with high b2-m serum level. Moreover, the results of our study suggest that progression of disease may be the results of in-vivo activation of the cells and lends support to previous studies showing that CLL cells are G0 cells with a potential to progress in the cell cycle after stimulation.