Binding of B cell chronic lymphocytic leukemia (B-CLL) cells to other
cells and to extracellular matrices influences the pathophysiology and
the clinical presentation of the B-CLL disease. It is still unknown w
hich adhesion pathways regulate the traffic of B-CLL cells within dist
inct histologic compartments of lymphoid organs. In addition, it is no
t yet clarified which mechanisms mediate the intercellular adhesion of
B-CLL cells. The present study sought to identify the mechanisms that
are involved in the binding of B-CLL cells to secondary lymphoid orga
ns in situ and in the homotypic aggregation of these cells. B-CLL cell
s specifically bound to germinal centers of normal human tonsils via t
he adhesion pair integrin alpha 4 beta 1/vascular cell adhesion molecu
le-1 (VCAM-1). Among a large panel of antibodies tested only mAbs agai
nst CD19 induced homotypic adhesion of B-CLL cells via the adhesion mo
lecules integrin alpha(L) (leukocyte function antigen-1 (LFA-1)), inte
rcellular adhesion molecule-1 (ICAM-1) and CD21. Anti-CD19-induced agg
regation required protein synthesis. We hypothesize that the observed
heterotypic and homotypic adhesion of B-CLL cells reflects the ability
of these leukemic cells to migrate in vivo.