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

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.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-017-0411-z) contains supplementary material, which is available to authorized users.

Update onActinobacillus pleuropneumoniae-knowledge, gaps and challenges

“…Among pro‐inflammatory cytokines, IL‐6 was found to be reliable both for monitoring bacterial infections in pigs (Fossum et al., ) and for evaluating the efficacy of antibiotic treatments (Lauritzen et al., ). Additionally, an induction of IL‐17, as indicated by both transcriptional and protein expression levels, has been observed during App infection (Brogaard et al., ; Sassu, Ladinig, et al., ).…”

“…Doses of 10 3–10 CFU of the same App serovar 2 strain were given intratracheally to fattening pigs, and a dose of 10 3 CFU found to be adequate for the development of clinical signs and lung alterations, but not death (Hennig‐Pauka et al., ). The adequate dose of the same strain for intranasal infection was 4 × 10 4 CFU (Sassu, Ladinig, et al., ).…”

“…Moreover, a difference in variation of CD4:CD8 ratio was reported in pigs immunized with low or high doses of App (Appleyard, Furesz, & Wilkie, ), and CD8α‐γδ T cells were found to be increased in BALF after contact with bacterial antigen (Faldyna et al., ). Recently, the frequency of Th17 cells in blood and lungs of pigs chronically infected with App was shown to positively correlate with the presence of lung lesions and antibody titres (Sassu, Ladinig, et al., ). Whether the presence of specific T cells initiates the immune evasion of App, leading to its retreat to tissue sites that are less accessible to immune cells, needs to be further investigated.…”

Evaluation of two DNA extraction techniques in the detection of Mycoplasma hyopneumoniae by PCR in lungs samples of pigs with and without pneumonia

“…The presence of samples with lesions, but negative for PCR, probably occurred due to infection by other respiratory agents, such as Actinobacillus pleuropneumoniae and Mannheimia haemolytica. These microorganisms are causative agents of respitatory disease in pigs and may cause similar lesions caused by M. hyopneumoniae (SASSU et al, 2017). Li et al (2019) observed a relationship between the presence of lesions and positivity in PCR.…”

Quantification and phenotypic characterisation of peripheral IFN-γ producing leucocytes in chickens vaccinated against Newcastle disease

“…Furthermore, only a few antibodies specific for chicken IFN-γ (chIFN-γ) are currently commercially available ( Table 1 ). In other domestic species such as pigs and cattle, the ICS method has been used with success in differentiating cells based on phenotypic and cytokine profile following polyclonal stimulation and antigen specific stimulation ( Sassu et al, 2017 , Sopp and Howard, 2001 ). The purpose of the present study was therefore to further evaluate, optimise and develop protocols for analyses of the chicken cellular response of not only polyclonal stimulation but also antigen-specific stimulation of Newcastle disease virus (NDV) specific T cells.…”