When the levels of metalloproteinase 9 (MMP-9) were measured, a statistically significant increased expression was observed in response to the serotype a (p = 0.0158), b (p = 0.0187), and c (p = 0.0052) with respect to non-infected condition at 2 h of stimulation, and in response to serotype a (p = 0.0002), b (p < 0.0001) and c (p = 0.0033) compared with the control condition after 24 h of infection. The gene discussed is MMP9; the disease is infection.