still getting sicker, the CD3+ lymphocytes present in the BALs of mice infected with v176-WT showed a reduced expression of activation markers CD69 and CD25, com- pared with control groups. This was consistent with the greater and earlier recruitment of lymphocytes, so that the immune response was already declining by day 7. It is unclear why a poxvirus would encode a protein that decreases virus virulence. One possibility is to prevent the virus from overwhelming its host too quickly. Another is that the v-slfn protein affects virus virulence differently in other models of infection and, consistent with this, v-slfn did not affect virulence in the intradermal model (Supple- mentary Fig. S3, available in JGV Online). VACV WR gene B15R, which encodes a soluble interleukin-1b receptor, is another example of a gene that decreases viral virulence in one model but not others (Alcami & Smith, 1992, 1996; Spriggs et al., 1992; Tscharke et al., 2002; Staib et al., 2005). 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