PTX3 and infection: Since the instillation of as low as 1 μg of PTX3 was sufficient to induce an antibacterial effect when administrated locally just before the infection (Figure 4E), we incubated 5 × 104 CFU of S. pneumoniae serotype 3 (i.e. the inoculum normally used for a lethal infection in our model) with 33.3 μg/ml of recombinant PTX3.