IFNB1 and infection: Of note, IL-4 expression in LTβR−/− animals was increased more than 10-fold before infection when compared to WT animals and this expression decreased markedly early after infection (days 7 and 12), followed by a distinct but transient increase on day 14 p.i. IFNβ expression levels in WT animals showed a 20-fold increase on day 12 p.i. (Figure 8(f)).