rCVB3.6 established a productive infection in these mice, however, because high fecal titers (0.41–1.27×106 PFU/g) were measured on day 2 p.i. Furthermore, rCVB3.6 infection induced the expansion of SMARTA cells in these same hosts (Figure 3, bottom right), indicating that the N-terminal component of the rCVB3.6 polyprotein, containing the CD8+ and CD4+ T cell epitopes, was present in sufficient abundance to trigger expansion of naïve SMARTA cells. Here, CD4 is linked to infection.