Analysis of the activation state of alpha4beta1 integrin in human B cell lines derived from myeloma, leukemia or lymphoma.

Myeloma cells specifically localize in the bone marrow and rarely circulate in blood. To study whether this immobilization could be partially explained by the presence of constitutively activated integrins, particularly alpha4beta1, we used the activation reporter HUTS-21 anti-beta1 mAb. These analyses showed that beta1 integrins on myeloma cells were moderately active and could be upregulated similarly to integrins on lymphoma or leukemia cells. Myeloma cells were also tested for their ability to attach to RGD-containing fibronectin fragments, a property of activated (but not resting) alpha4beta1. Two cell lines adhered to these fragments and this was inhibited by anti-alpha5 but not by anti-alpha4 mAbs. These results show that myeloma cells bear low/moderately active alpha4beta1 and support the notion that multiple interactions contribute to their localization in the bone marrow.