Innate and Adaptive T cell Immunity to Campylobacter jejuni

Source:

Edwards LA, Nistala K, Mills DC, Stephenson HN, Zilbauer M, Wren BW, Dorrell

N, Lindley KJ, Wedderburn LR, Bajaj-Elliott M. Delineation of the Innate and

Adaptive T-Cell Immune Outcome in the Human Host in Response to Campylobacter

jejuni Infection. PLoS One. 2010 Nov 9;5(11):e15398. PubMed PMID: 21085698.

 

Campylobacter jejuni is one of the most common causes of gastroenteritis in the world. Infection with this bacteria results in clinical symptoms that can range from mild diarrhea to severe inflammatory enteritis. It has also been linked to subsequent development of Guillain-Barre syndrome (GBS). Due to significant morbidity caused by it in children in the developing world and due to emergence of antibiotic resistant clinical isolates, there is a need to further understand C. jejuni mediated pathogenesis.

There are some obstacles associated with the study of pathogenesis of and immunity to this pathogen. These are a) no convenient animal model of infection is available, b) it is unethical to perform human studies due to risk of volunteers developing GBS, c) C. jejuni mediated gastritis is self limited d) there is added risk of intestinal perforation due to which it is difficult to investigate immunity to infection in situ.

The present study is conducted by investigators at Institute of Child Health, London School of Hygiene and Tropical Medicine and Addenbrooke's hospital, Cambridge. In this study, the authors used an ex vivo model of infection which is based on human pediatric small intestine and colonic pinch biopsies in the co-culture system and looked for cytokine production in response to C. jejuni infection. This in vitro organ culture system (IVOC) has earlier been used to study enteropathogenic E. coli infection.

Previous studies have shown C. jejuni mediated effects on murine and human DC. However, the effect of this interaction of bacteria and DC on human T cells is not known. Thus, the second objective of this work was to look at the impact of bacterial-driven dendritic cell activation on T –cell mediated immunity.

Results:

1. Ex-vivo colonization of human intestine by C. jejuni: The investigators first sought to determine whether C. jejuni was able to colonize human gut explants tissue in the IVOC model of infection. Thus, they co-cultured human intestinal biopsies from the terminal ileum with wild type (WT) C. jejuni 11168H. Following this, bacteria were localized by immuno-labeling with primary un-labeled anti-Campylobacter antibody and secondary FITC-conjugated antibody. Confocal microscopy revealed that C. jejuni was routinely found in close association with the epithelial lining.
   
2. Ex-vivo release of mucosal cytokines in response to C. jejuni infection: Pediatric terminal ileum and colonic biopsy tissue were exposed to WT C. jejuni and post-infection production of cytokines was determined. The majority of cytokines were undetectable or minimally expressed in uninfected tissue. Post infection, IFN-gamma showed the most significant induction in both the tissues. IL-22 was secreted spontaneously by both tissues. IL-17 induction was modest. Among cytokines known to influence T cells, IL-23 showed the most significant increase. In contrast, increase in IL-12 and IL-6 was intermediate.
   
3. C. jejuni wild type strain drive an IL-23/Il-12 response in monocyte-derived dendritic cells: The authors next sought to determine the effect of C. jejuni infection on DC cytokine responses. They particular focused on IL-12 family members as they are critical mediators in defining the molecular nature of downstream T cell immunity. The IL-12 family members (IL-12, IL-23, IL-27 and IL-35) are known to share subunits. IL-12 is composed of p35 and p40, IL-23 is composed of p40 and p19, IL-27 is composed of p28 and Epstein Barr virus induced gene 3 (EBI3). The investigators exposed DCs to WT C. jejuni and investigated the expression of IL-12 family subunits by real time PCR. They observed that majority of individuals showed expression of p19, p35, p40 and EBI3 subunits in response to infection, but none of them showed induction of p28. The authors further quantified the cytokine response by ELISA and observed that IL-12, IL-23, IL-1beta and IL-6 were undetectable in DCs exposed to medium alone. In contrast, all four cytokines were induced in the presence of WT C. jejuni.
   
4. C. jejuni-infected DCs generate a cytokine milieu that favors single Th-17, Th-1 and double Th-17/Th-1 positive T cell responses: The authors further tested the ability of supernatants from infected DCs to propagate CD4+CD45RO+ T cell effector responses. They enriched the PBMCs for CD4+CD45RO+ memory T cells and stimulated with anti-CD3, anti-CD28 coated beads for 5 days in the presence of supernatants taken from DCs cultured with medium alone or with WT C. jejuni. They performed flow cytometric analysis and found an increase in single positive IL-17A and IFN-gamma producing T cells and a preferential increase in IL-17A/IFN-gamma double positive T cells. The authors also confirmed the increase in IFN-gamma and IL-17 protein levels by ELISA.
   
5. T-cell derived IL-22 expression in response to C. jejuni infection: The main source of IL-22 is innate immune cells. However, its expression has also been known to be associated with Th-1, Th-17 and a distinct Th-22-cell subtype. The authors therefore investigated whether C. jejuni infection results in T cells producing IL-22. They performed same experiments as mentioned above and observed that T cell mediated IL-22 expression was indeed observed in the presence of infected DC supernatants.
   
6. IL-17A and F modulate number of intracellular C. jejuni in intestinal epithelia: Based on the results, the authors hypothesized that in addition to well-established bactericidal and tissue repair functions of IFN-gamma, IL-22 and IL-17, these cytokines may also modulate adhesion and invasion of intestinal epithelial cells (IEC) by C. jejuni. To test this hypothesis, they incubated polarized Caco-2 cells with IFN-gamma, IL-17A, IL-17F or IL-22 for 24 hours and then infected the cells with C. jejuni. At three hours post infection, the investigators performed a standard bacterial adhesion and invasion assay. None of the cytokines were able to modify the number of C. jejuni bacterial cells that adhered to IEC. IL-17A and in particular IL-17F caused reduction in number of viable intracellular bacteria. In contrast, IFN-gamma or IL-22 had no effect on number of viable intracellular bacteria.