**3.2 Active targeting**

In addition to the potential for passive targeting, the two primary cell types found within the pannus tissue, rheumatoid arthritis synovial fibroblasts (RASFs) and rheumatoid arthritis synovial macrophages (RASMs) selectively express surface receptors, such as CD44 (Haynes et al., 1991; Johnson et al., 1993), folate receptor (Nagayoshi et al., 2005; van der Heijden et al., 2009), and integrin V3 (Wilder, 2002) that are candidates for active targeting. Angiogenic vascular endothelial cells (VECs) are also present as a result of neovascularization, and the E-selectin adhesion molecule has been identified as another viable target for drug delivery (Jamar et al., 2002).
