IL4 and influenza: To better understand the effect of probiotic strain C. butyricum S-45-5 on immune modulation upon influenza infection, we measured local (lung) and systemic (serum) expression of pro-inflammatory (IL-6, IL-12, TNF-α, and IL-1β) and anti-inflammatory (IL-4, IL-10) cytokines at four different days following influenza infection (Figure 5A).