- Tat protein is an HIV-1-encoded beta-chemokine homolog that promotes migration and up-regulates CCR3 expression on human Fc epsilon RI+ cells. de Paulis, A., De Palma, R., Di Gioia, L., Carfora, M., Prevete, N., Tosi, G., Accolla, R.S., Marone, G. J. Immunol. (2000)