Immune Response to and Histopathology of Campylobacter jejuni Infection in Ferrets (Mustela putorius furo)

Campylobacter jejuni is 1 of the most common enteric bacterial pathogens worldwide. The mechanisms of pathogenesis remain obscure, in part because of limitations of small animal models. Young ferrets develop diarrhea when fed C. jejuni, but their pathology and the immune response after infection have not been examined in detail. In the present study, we examined the pathogenesis of C. jejuni CG8421 and associated immune responses in ferrets. After oral infection with C. jejuni CG8421, 86.7% of the animals developed diarrhea and inflammatory responses that were similar to those seen in human infection. Pronounced histopathologic changes in the colonic mucosa of infected animals were observed during the acute phase (days 1 through 3) of infection. Electron micrographs of colonic epithelium revealed disruption of the villi and internalized bacteria that were not within membrane vacuoles. During the acute phase, C. jejuni was isolated from the livers of 7 of 9 (78%) animals, and bacteria were visualized immunohistochemically in the livers from 5 of the 7 animals (71%) from which C. jejuni was isolated. A vigorous systemic and mucosal immune response to Campylobacter antigens was elicited after infection of ferrets. The data presented contribute to the current knowledge of the pathogenicity of and immunologic response to C. jejuni CG8421 in ferrets and better understanding of this model.Abbreviation: ASC, antibody-secreting cellsCampylobacter jejuni are gram-negative, spiral, microaerophilic, motile bacteria and 1 of the most common enteric bacterial pathogens globally.^15,20 The annual incidence of C. jejuni diarrheal disease varies geographically, ranging from sporadic infections in young adults in developed countries²⁸ to as frequent as 40,000 per 100,000 among children living in hyperendemic regions.¹⁵ In addition, C. jejuni is the primary cause of ‘traveler''s diarrhea’ in various regions of the world.^39,41,44 The clinical disease of C. jejuni infection has a wide spectrum of symptoms, varying from a mild, transient watery diarrhea to a bloody diarrhea with severe abdominal cramps and fever. C. jejuni infection also is associated with development of Guillain–Barré syndrome.⁵¹ Most strains of C. jejuni contain lipooligosaccharides that mimic human gangliosides structurally. Antibodies against these lipooligosaccharide structures lead to an autoimmune response, resulting in Guillain–Barré syndrome.⁵²Despite extensive study, little is understood about the mechanism by which C. jejuni causes diarrheal disease. Various Campylobacter small animal models have been reported, but these require surgical manipulation,^13,46 administration of chemicals or antibiotics (or both),^17,26,30 or inoculation by an unnatural route.⁵ None of these published models incorporate the natural route of infection. Although several immunodeficient mouse models have been reported,^35,36,49 the applicability of these models for studying the pathogenesis and immune response of natural infection is limited. An adult mouse lung model has been described that may be useful for studying pathogenesis and inflammatory response and acquired immunity, but the route of infection is not the same as that in humans.^1,5 Unlike other small animals, naïve ferrets (younger than 11 wk) intragastrically inoculated with C. jejuni developed mild to moderate diarrhea with mucus, fecal leukocytes or frank blood that lasted for as long as 3 d and remained colonized for as long as 8 d.^9,10,18 Moreover, on rechallenge with the homologous bacterial strain, ferrets asymptomatically excreted C. jejuni in their stools.¹⁰ The observation of resistance to disease, but not to infection, is similar to findings from human studies, in which protection against disease developed before colonization resistance.¹¹ Ferrets have been used to evaluate vaccines against C. jejuni¹⁴ and in molecular pathogenesis studies using strain 81-176 to confirm a role in virulence for capsular polysaccharide and flagellar glycans.^3,21 However, we evaluated the histopathology and immune response after C. jejuni infection in ferrets in more detail in the present study.C. jejuni CG8421 was isolated from a case of dysentery in Thailand. It has an lipooligosaccharide core that, as shown by chemical analyses, lacks all ganglioside mimicry.³⁸ The absence of ganglioside mimicry is predicted to reduce the risk of Guillain–Barré syndrome. We selected strain CG8421 for the current studies as part of an evaluation of a potential strain for use in future human vaccine challenge studies. Here we report the pathogenesis, histopathology, inflammatory, and immune responses after oral infection of ferrets with C. jejuni strain CG8421.