Decreased LCMV-Cl13 titers following Rb treatment coincided with upregulation of the costimulatory molecules B7-1 and B7-2 on dendritic cells (DCs; Figure 3B) and other antigen presenting cell (APC) populations (B cells and macrophages) [8], suggesting that prolonged or repeated costimulatory interactions during chronic viral infection might sustain T cells when virus loads are reduced. Here, RB1 is linked to viral infectious disease.