Methods: Flow cytometry was used to quantify cell surface expression of sLeX, b2 integrin and other adhesion molecules. Flow chamber adhesion experiments were used to investigate the functional significance of adhesion molecule expression.
Results: 7/10 OSCC cell lines tested expressed significant levels of sLeX, but not b2 integrins. Normal oral keratinocytes (NOK) expressed neither. The SCC4 cell line was a minimal sLeX expressor and Cal27 a high expressor. Cal27 but not NOK or SCC4, exhibited significant levels of tethering, rolling and firm adhesion to EC at rates of flow similar to those in post capillary venules (1.5 Dynes/cm2). Blockade of binding with anti-E-selectin and anti-sLeX antibodies confirmed their role in the binding process. This was also confirmed by demonstrating Cal 27 binding to CHO cells transfected with E-selectin and E-selectin coated plastic. E-selectin normally mediates rolling of leukocytes on EC but not the arrest and firm adhesion required for transmigration. This is mediated by b2 integrins. Suprisingly, on OSCC sLeX was able to mediate arrest and firm adhesion, as well as rolling, in the absence of b2 integrin expression.
Conclusions: These observations suggest that some OSCC may aquire the ability to adhere to vascular endothelium under conditions of flow by expressing sLeX. This could enable them to leave the circulation to form metastatic deposits.