In terms of the expression of IL-18 by THP-1 macrophage cells, the three serotypes analyzed were able to induce a statistically significant expression of this cytokine with respect to the control condition serotype a (p = 0.0056), b (p = 0.0051) and c (p = 0.0190) at 2 h of infection and serotype a (p = 0.0074), b (p = 0.0017) and c (p = 0.0002) at 24 h of infection. Here, IL18 is linked to infection.