Thus, implementing the “combined PMN migration and Shigella invasion” model, we observed that following apical infection of T84 monolayers with WT S. flexneri in the presence of AAT at concentrations between 1 and 100 nM, both PMN transepithelial migration (Fig. 3A) and bacterial invasion (Fig. 3B) significantly increased. Here, SERPINA1 is linked to infection.