We show that major histocompatibility complex (MHC) class II molecules on B cells transit signals which regulate adhesion in a negative manner. Engagement of MHC class II molecules with antibodies results in detachment of B cells previously bound to interferon-gamma-activated human umbilical cord venous endothelial cells. This process depends on metabolic energy, active signaling and protein tyrosine kinase activity. The adhesion pathway influenced by this signaling event is neuraminidase sensitive. The anti-adhesive signaling program is activated in B cell lines with a mature phenotype, e.g. normal B cells from spleen and tonsil. In contrast, cell lines with a pre-B cell phenotype and normal B cells from peripheral blood are refractory to MHC class II-mediated regulation of adhesion. These results extend to neoplastic cells from patients with lymphoproliferative diseases representing different stages of B cell maturation. These results suggest that MHC class II-mediated signals regulate B cell adhesion in a developmentally programmed fashion; this might have implications for clinical behavior of B cell malignancies.