The Effect of Helicobacter hepaticus Infection on Immune Responses Specific to Herpes Simplex Virus Type 1 and Characteristics of Dendritic Cells

Infection of mice with Helicobacter hepaticus is common in research colonies, yet little is known about how this persistent infection affects immunologic research. The goal of this study was to determine whether H. hepaticus infection status can modulate immune responses specific to herpes simplex virus type 1 (HSV1) and the phenotypic and functional characteristics of dendritic cells (DC) of mice. We compared virus-specific antibody and T cell-mediated responses in H. hepaticus-infected and noninfected mice that were inoculated intranasally with HSV1. The effect of H. hepaticus on the HSV1-specific antibody and T cell-mediated immune responses in superficial cervical and tracheobronchal lymph nodes (LN) did not reach statistical significance. Surface expression of the maturation-associated markers CD40, CD80, CD86, and MHC II and percentages of IL12p40- and TNFα-producing DC from spleen and colic LN in H. hepaticus-infected mice and noninfected mice were measured in separate experiments. Expression of CD40, CD86, and MHC II and percentages of IL12p40- and TNFα-producing DC from colic LN were decreased in H. hepaticus-infected mice. In contrast, H. hepaticus infection did not reduce the expression of these molecules by splenic DC. Expression of CD40, CD80, CD86, and MHC II on splenic DC from H. hepaticus-infected mice was increased after in vitro lipopolysaccharide stimulation. These results indicate that H. hepaticus infection can influence the results of immunologic assays in mice and support the use of H. hepaticus-free mice in immunologic research.Abbreviations: DC, dendritic cells; HSV1, herpes simplex virus type 1; LN, lymph nodes; MHC II, major histocompatibility complex class II; MHV, mouse hepatitis virus; OVA, ovalbumin peptide SIINFEKL; PE, phycoerythrinHelicobacter hepaticus is a gram-negative, microaerophilic, curved to spiral-shaped bacterium with bipolar, sheathed flagella. H. hepaticus was described for the first time in 1994 as the cause of chronic active hepatitis associated with a high incidence of hepatocellular neoplasms in mice on a long-term toxicology study.³⁹ Since then, H. hepaticus has been identified as a common contaminant of mouse colonies at a variety of research institutions. Although commercial breeders produce H. hepaticus-free animals, many mouse colonies at public and private research institutions still harbor H. hepaticus. A recent survey found H. hepaticus-infected mice in 59% of commercial and academic institutions in Canada, Europe, Asia, Australia, and the United States.³⁵H. hepaticus persistently colonizes the hepatic bile canaliculi and the cecal and colonic mucosa of mice.^9,39 Infection can cause chronic active hepatitis, hepatocellular neoplasms, and typhlocolitis, which vary in severity depending on the strain, age, gender, and immune status of the mouse.^5,9,11,39 In adult immunocompetent mice, H. hepaticus infection is usually asymptomatic. However, immune-dysregulated mice can develop inflammatory bowel disease, which may present as rectal prolapse or diarrhea.¹⁶Mice initiate immune responses against H. hepaticus primarily through its interaction with Toll-like receptor 2 on antigen-presenting cells.²¹ Both systemic and local (at the site of infection) H. hepaticus-specific Th1-type immune responses are induced in immunocompetent mice.^26,40 Systemic antibody and cell-mediated immunity against the bacteria persist for at least 46 wk after experimental inoculation.⁴⁰ Gene expression profiles of cecal tissue of H. hepaticus-infected mice have shown that inflammatory responses differ depending on the mouse strain. For example, A/JCr mice had significant and prolonged expression of the Th1-type cytokines IFNγ and IL12p40 in cecal mucosa, and these expression levels persisted for at least 3 mo after H. hepaticus infection. However, C57BL/6 mice had a lesser elevation of IFNγ gene expression without an effect on IL12p40. IFN γ expression waned by 1 mo after inoculation in C57BL/6 mice.²⁵ In addition, H. hepaticus-specific secretory IgA antibodies are persistently detected in the feces of mice.⁴⁰ How these immune responses in H. hepaticus-infected mice might affect immunologic research is unknown.The goal of this study was to determine whether immune responses to herpes simplex virus type 1 (HSV1) and the phenotypic and functional characteristics of dendritic cells (DC) are altered in H. hepaticus-infected mice. The intranasal HSV1 infection model is used widely to study immune mechanisms in mice. Immunity to HSV1 consists of virus-neutralizing antibodies in the serum and virus-specific T cells in the draining LN. Superficial cervical and mediastinal LN have been described as draining LN for intranasal HSV1 infection.² The response to HSV1 infection peaks at 7 d after infection and leads to clearance of the viral load.² In this study, we compared levels of HSV1-specific antibody and T cell-mediated immune responses between H. hepaticus-infected and noninfected mice.Dendritic cells are important components of the immune system that play a role in antigen processing and presentation. On exposure to foreign antigen, DC mature and express increased levels of major histocompatibility complex class II proteins (MHC II), CD40, CD80, and CD86 on the cell surface. These maturation-associated cell surface markers interact with naive T and B cells to initiate antibody- and cell-mediated immune responses against foreign antigens.²⁷ In addition, mature DC secrete proinflammatory cytokines, including TNFα and IL12p40. These cytokines lead to increased vascular permeability, complement activity, lymphocyte activation, lymphocyte proliferation, and increased antibody production.²⁷ To determine whether infection with H. hepaticus affects characteristics of DC, we measured the expression of the maturation-associated cell surface markers CD40, CD80, CD86, and MHC II and proinflammatory cytokines IL12p40 and TNFα by DC derived from the spleen and colic LN of H. hepaticus-infected and noninfected mice. Our findings indicate that H. hepaticus infection can influence the various aspects of immune responsiveness and, therefore, must be considered as a potential variable in studies in which immune function is a measurable outcome.