CRK and bacterial infectious disease: Work from our lab and others have implicated more receptors and signaling pathways in P. aeruginosa entry or host responses to bacterial infection, including PDGFR, Abl/Crk [31], and Src family kinases [61], e.g. Lyn [62], and it will be of interest to determine if any of these molecules are differently activated upon Tfp- or flagella-mediated binding at the AP or BL surface of polarized epithelium.