Frequency of Th17 cells correlates with the presence of lung lesions in pigs chronically infected with Actinobacillus pleuropneumoniae

Elena L Sassu,Isabel Hennig-Pauka,Barbara Richter,Heiko Stein,Maria Stadler,Wilhelm Gerner,Christian Knecht,Janna Frömbling,Monika Ehling-Schulz,Andrea Ladinig,Joachim Spergser,Robert Graage,Stephanie C Talker

doi:10.1186/s13567-017-0411-z

Elena L Sassu, Isabel Hennig-Pauka + Show 11 more

Open Access

https://doi.org/10.1186/s13567-017-0411-z

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Abstract

Porcine contagious pleuropneumonia caused by Actinobacillus pleuropneumoniae (APP) remains one of the major causes of poor growth performance and respiratory disease in pig herds. While the role of antibodies against APP has been intensely studied, the porcine T cell response remains poorly characterized. To address this, pigs were intranasally infected with APP serotype 2 and euthanized during the acute phase [6–10 days post-infection (dpi)] or the chronic phase of APP infection (27–31 dpi). Lymphocytes isolated from blood, tonsils, lung tissue and tracheobronchial lymph nodes were analyzed by intracellular cytokine staining (ICS) for IL-17A, IL-10 and TNF-α production after in vitro stimulation with crude capsular extract (CCE) of the APP inoculation strain. This was combined with cell surface staining for the expression of CD4, CD8α and TCR-γδ. Clinical records, microbiological investigations and pathological findings confirmed the induction of a subclinical APP infection. ICS-assays revealed the presence of APP-CCE specific CD4+CD8αdim IL-17A-producing T cells in blood and lung tissue in most infected animals during the acute and chronic phase of infection and a minor fraction of these cells co-produced TNF-α. APP-CCE specific IL-17A-producing γδ T cells could not be found and APP-CCE specific IL-10-producing CD4+ T cells were present in various organs but only in a few infected animals. The frequency of identified putative Th17 cells (CD4+CD8αdimIL-17A+) in lung and blood correlated positively with lung lesion scores and APP-specific antibody titers during the chronic phase. These results suggest a potential role of Th17 cells in the immune pathogenesis of APP infection.

Highlights

Actinobacillus pleuropneumoniae (APP) is a gram negative bacterium, belonging to the Pasteurellaceae family that causes porcine respiratory disease worldwide
IL-17 was shown to be induced on the transcriptional level in lungs of pigs affected by APP [14] and it has been demonstrated that CD4+ and γδ T cells are capable to produce IL-17 in swine [15,16,17]
We found that the majority of pigs infected with APP harbor APP-crude capsular extract (CCE) specific IL-17A+ CD4+ T cells in the lung and in the blood during the acute and the chronic phase of APP infection

Summary

Introduction

Actinobacillus pleuropneumoniae (APP) is a gram negative bacterium, belonging to the Pasteurellaceae family that causes porcine respiratory disease worldwide. In vivo and in vitro studies with Mannheimia haemolytica, which like APP belongs to the Pasteurellaceae family and induces neutrophilic infiltration in the lung, suggested an IL-17 production by bovine γδ T cells [20]. Since the anti-inflammatory cytokine IL-10 may support the survival of microorganisms in the host via inhibiting their cell-mediated immune response [21,22,23], we investigated in parallel its role in persistence of APP. To address these issues we developed an APP infection model and an in vitro stimulation assay making use of an APP crude capsular extract (APP-CCE). The frequency of these cells in lung and peripheral blood was found to correlate positively with lung lesions and APP-specific antibody titers

Materials and methods

Results

Discussion