- Major histocompatibility complex class I molecules are down-regulated at the cell surface by the K5 protein encoded by Kaposi's sarcoma-associated herpesvirus/human herpesvirus-8. Haque, M., Ueda, K., Nakano, K., Hirata, Y., Parravicini, C., Corbellino, M., Yamanishi, K. J. Gen. Virol. (2001)