GSE136893
Establishment of chronic typhoid infection in a mouse carriage model involves a Type 2 immune shift and T and B cell recruitment to the gallbladder
Typhoid fever, caused primarily by Salmonella enterica serovar Typhi (S. Typhi), is a life-threatening systemic disease responsible for significant morbidity and mortality worldwide. 3-5% of individuals infected with S. Typhi become chronic carriers due to bacterial persistence in the gallbladder. We have demonstrated that Salmonella forms biofilms on gallstones to establish gallbladder carriage. However, an in-depth molecular understanding of chronic carriage in the gallbladder, from the perspective of both the pathogen and host, is poorly defined. To examine the dynamics of the gallbladder in response to Salmonella infection, we performed transcriptional profiling in the mouse gallbladder at early (7 day) and chronic (21 day) time points. RNA-Seq revealed a shift from a Th1 pro-inflammatory response at 7 days post infection (DPI) towards an anti-inflammatory Th2 response by 21 DPI, characterized by increased levels of immunoglobulins and the Th2 master transcriptional regulator, GATA3. Additionally, bioinformatic analysis predicted the upstream regulation of characteristic Th2 markers including IL-4 and Stat6. Immunohistochemistry and FACS analysis confirmed a significant increase in lymphocytes, including T and B cells, at 21 DPI in mice with gallstones. Interestingly, Salmonella-specific CD4 T-cells were ten-fold higher in the gallbladder of mice with gallstones at 21 DPI. We speculate that the biofilm state allows Salmonella to resist the initial onslaught of the Th1 inflammatory response, while yet undefined events influence a switch in the host immunity towards a more permissive Type 2 response, enabling the establishment of chronic infection. Overall design: 48 male 129X1/SvJ mice were fed a lithogenic diet (1% cholesterol and 0.5% cholic acid (Envigo/Harlan Laboratory, IN, USA)) for 8 weeks, half were injected intraperitoneally (IP) with PBS (mock infection control) and half were inoculated IP with a dose of 2x10e4 CFUs of S. Typhimurium. Half the mice from each group were sacrificed at 7 DPI and the remaining half at 21 DPI. At both time points gallbladders were removed and flash frozen in dry ice for RNA extraction, gallbladders from 3 animals were pooled to make one sample. Only RNA samples that met quality standards were sequenced.