The type IV pathway has been identified in lrgionclla pncunmphila and Helicobacter pylori to secrete toxin proteins into the host cells. Peptide secreted through this pathway is exported through the cytoplasmic membrane by the GSP system. The periplasmic inter- mediate is secreted into the host cell by a similar mechanism as in the type III pathway. However. the outer membrane channel of the type IV pathway is not homologous with that ofthe type III pathway (Figure 3.15).