Doctor of Philosophy (PhD)


Veterinary Medical Sciences - Pathobiological Sciences

Document Type



Bacterial pneumonia and sepsis are two important causes of mortality in the world. Emergence of multidrug resistant bacteria has necessitated the development of new treatment and/or prevention strategies to augment host immune defense. In this context, the innate host defense is critical in clearing pathogenic bacteria from the host. Early neutrophil recruitment is a critical step in a multistep requence leading to bacterial clearance. Pattern recognition receptors (PRRs) play a critical role in the innate immune system. Receptor interacting protein 2 (RIP-2) is an adaptor for the nod-like receptors (NLR) NOD1 and NOD2. Nucleotide oligomerisation domain 2 (NOD2) is an intracellular PRR that is shown to be important for host defense against intracellular bacterial pathogens. However, the role of NOD2 and RIP-2 during Gram-negative bacterial pneumonia and polymicrobial sepsis has not been explored. Thus, we hypothesize that the NOD2/RIP-2 axis is critical for host defense during bacterial pneumonia and sepsis/septic peritonitis. To test this hypothesis, we infected NOD2(NOD2-/-), RIP-2(RIP-2-/-) deficient mice intratracheally (i.t) with E. coli (106 CFUs/mouse) and Klebsiella pneumoniae (103 CFUs/mouse). We observed that NOD2/RIP2 signaling is critical for the host defense during gram-negative pneumonia and poly microbial sepsis. The NOD2/RIP2 axis regulates neutrophil recruitment via IL-17A production. We also found that NOD2/RIP-2 signaling is essential for the production of IL-6 and activation of STAT3. We demonstrated that RIP-2 regulates inflammasome activity that is independent of NOD2 signaling. Taken together, these data demonstrate that the NOD2/RIP-2 axis plays a critical role in neutrophil-mediated host defense through IL-17A production and by inflammasome activation. In cecal ligation puncture (CLP) induced sepsis, RIP2-/- mice show increased mortality with higher bacterial burden in the peritoneum and systemic organs compared to WT controls. We found reduced neutrophil influx IL-17A and IL-1beta levels in the peritoneum of RIP2-/- mice after CLP. Furthermore, we also observed increased systemic inflammation accompanied by vital organ damage in the knockout mice. As a whole our data suggest a critical role of RIP2 in neutrophil recruitment, along with IL-17A and IL-1beta during sepsis.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Jeyaseelan, Samithamby