Ephrin receptors and ligands also play important roles in KSHV pathogenesis; EphA2 and EphA4 receptors and Ephrin-B2 ligands are abundantly expressed in KS cell lines and tumor biopsies, and Ephrin-B2 acts as an essential factor in KS cell viability and tumor growth [16, 17]. This evidence concerns the gene EFNB2 and Kaposi's sarcoma.