CD44 and neoplasm: To explore the effect of protein corona on tumor cell internalization, the expression level of integrin receptor for OPN binding and transmembrane CD44 on A549, HeLa, and human umbilical vein endothelial cells (HUVEC) was determined, and the results showed that integrin and CD44 were highly expressed on the surface of A549 and HeLa cells, but were low in normal HUVEC cells (Fig. 8a).