Role of Rapid IFNg Secretion by CD8+ T Cells in Clearance of Food Borne Listeria

Listeria monocytogenes (Lm) is important an important pathogen to study because: 1) it causes life threatening food borne infections of significant public health concern, 2) it is a genetically tractable organism with a unique intracellular lifestyle used as a tool for understanding the cell biology of mammalian cells, and 3) systemic (i.v) listeriosis is a highly reproducible infection frequently used by immunologists to study cell- mediated immune responses. However, due to the lack of a good animal model for oral transmission of Lm, we still know very little about the infectious dose required to establish intestinal infection, mechanisms of spread from the gut, or why the innate susceptibility to developing severe gastroenteritis and systemic listeriosis varies among individuals. We recently developed a new model of oral Lm infection using mice fed contaminated food. This natural feeding model revealed clear differences in the ability of Lm to colonize the gut and spread systemically in susceptible (BALB) vs. resistant (B6) mice. Thus, for the first time, we can now study how gut-adapted Lm that survive digestive processes in the stomach are able to colonize the intestinal mucosa and serve as a nidus for continual re-seeding of peripheral tissues in susceptible mice that are unable to quickly clear the gut infection. Since the vast majority of patients hospitalized with listeriosis can be considered immune compromised in some way, it has long been thought that protective immune responses were critical for limiting the infection to a self-limiting gastroenteritis in resistant individuals. Our central hypothesis predicts that one such innate immune mechanism is the rapid secretion of IFN? by a subset of memory phenotype CD8+ T cells. We postulate that this early IFN? response can limit the growth and spread of Lm in resistant individuals and that susceptible mice or humans who lack this ability will be more likely to develop life-threatening systemic listeriosis. We have three specific aims: (1) to identify the cell types that allow for exponential growth of Lm in the colons of susceptible BALB mice and thus serve as the targets of protective innate immune responses in resistant B6 mice; (2) to define the mechanisms whereby T cell derived IFN? can rapidly limit the intracellular growth of Lm in the colon; (3) to identify IFN?-dependent innate immune mechanisms that promote rapid clearance of Lm in peripheral tissues after dissemination from the gut. A key strategy in this proposal will be the use of a unique adoptive transfer system wherein T cells from a responsive mouse are injected into a MHC-matched non-responsive mouse. This powerful approach will allow us to specifically isolate the function of IFN? rapidly produced by CD8+ T cells while leaving all other innate immune mechanisms intact. These studies will have a large impact on both microbiologists and immunologists as we anticipate that our natural feeding model will be widely used by both groups in the future to identify mechanisms that promote either bacterial virulence or host resistance during infection.