Third, depletion of T cells, specifically CD4+ T cells, was sufficient to transform an abortive infection into an encephalitic infection, while depletion of CD8+ T cells had no effect (Iwasaki et al., 1977; Smith et al., 1982; Weiland et al., 1992; Xiang et al., 1995; Hooper et al., 1998; Galelli et al., 2000). Here, CD4 is linked to infection.