Diagram showing possible involvement of both CD46 and type 1 fimbrial receptor signalling in the internalisation of E. coli by PTECs. Internalisation of E. coli is initiated by type 1 fimberiae mediated adhesion to epithelium mannosylated glycoproteins receptor. This may be sufficient to induce internalisation alone. However, during UTI, E. coli can be opsonised by urine C3 in urinary tract space. C3b bound on bacteria surface interact with cell surface expressed CD46. This C3b-CD46 interaction could activate host cells and augments the direct interaction of fimH with manosylated receptor resulting in a high internalisation. Inhibition and FimH mutant experiments indicate that non-opsonic interactions are necessary for E. coli adherence to and invasion of PTECs.