Diarrheal disease caused by bacterial pathogens continues to be a major public health concern worldwide due to significant increases in mortality annually. Members of the Shigella genus contribute significantly to bacterial diarrheal incidences worldwide. Shigella is a Gram-negative facultative anaerobe that belongs to the family Enterobacteriaceae. They are considered highly infectious as only 10-100 organisms are required to cause disease. Like many other Gram-negative gut pathogens, Shigella utilizes a type III secretion system (T3SS) during infection to translocate bacterial effector proteins into host cells which interfere with host signaling pathways to benefit their survival. The exact function of many T3 effector proteins remains unknown. However recently, the T3SS effector EspL from enteropathogenic Escherichia coli (EPEC), was shown to contain a cysteine protease catalytic motif that targets and degrades the host RHIM domain containing proteins, RIPK1, RIPK3, TRIF and DAI, hence blocking inflammation and necroptotic cell death during infection. Homologues of EspL are also found in Shigella, namely: OspD2 and OspD3. Although previously labelled as Shigella toxins, the exact function of these effectors is yet to be elucidated. The primary aim of my study is to characterize the role of OspD2 and OspD3 and to determine their host cell targets. Co-transfection and co-immunoprecipitation experiments with OspD2 or OspD3 and the RHIM family of proteins suggest that OspD3, but not OspD2 targets and cleaves the RHIM family of proteins. Subsequent proteomap studies have led to the identification of several unique host cells targets for OspD2 and OspD3, suggesting the involvement of these proteins in the interferon signaling pathway. Currently, the exact roles of these proteins in the interferon signaling pathway are being studied. Once the functions of OspD2 and OspD3 in the interferon signalling pathway is known, the contribution of these proteins to host cell defence will be determined.