Degraded neutrophil extracellular traps promote the growth of Actinobacillus pleuropneumoniae

Abstract

Actinobacillus pleuropneumoniae (A.pp) causes severe pneumonia associated with enormous economic loss in pigs. Peracute diseased pigs die in <24 h with pneumonia. Neutrophils are the prominent innate immune cell in this infection that massively infiltrate the infected lung. Here we show that neutrophils release neutrophil extracellular traps (NETs) as response to A.pp infection. Numerous NET-markers were identified in bronchoalveolar lavage fluid (BALF) of A.pp-infected piglets in vivo, however, most NET fibers are degraded. Importantly, A.pp is able to enhance its growth rate in the presence of NETs that have been degraded by nucleases efficiently. A.pp itself releases no nuclease, but we identified host nucleases as sources that degrade NETs after A.pp infection. Furthermore, the nucleases of co-infecting pathogens like Streptococcus suis increase growth of A.pp in presence of porcine NETs. Thus, A.pp is not only evading the antimicrobial activity of NETs, A.pp is rather additionally using parts of NETs as growth factor thereby taking advantage of host nucleases as DNase1 or nucleases of co-infecting bacteria, which degrade NETs. This effect can be diminished by inhibiting the bacterial adenosine synthase indicating that degraded NETs serve as a source for NAD, which is required by A.pp for its growth. A similar phenotype was found for the human pathogen Haemophilus (H.) influenzae and its growth in the presence of human neutrophils. H. influenzae benefits from host nucleases in the presence of neutrophils. These data shed light on the detrimental effects of NETs during host immune response against certain bacterial species that require and/or efficiently take advantage of degraded DNA material, which has been provided by host nuclease or nucleases of other co-infecting bacteria, as growth source.

Role of Bacterial and Host DNases on Host-Pathogen Interaction during Streptococcus suis Meningitis

“…The authors observed an enhanced bacterial clearance in the CSF of infected rats by increased phagocytosis and NET degradation when treated with DNase 1. In contrast to this protective effect of DNase 1 in meningitis, it was found that the respiratory tract pathogens Actinobacillus pleuropneumoniae and Haemophilus influenzae survive even better in the presence of neutrophils treated with DNases, because degraded NETs release nutrients as NAD, which enhance bacterial growth [12].…”

“…A Pico Green quantification assay (Quant-iT™ PicoGreen ® ; Invitrogen, Carlsbad, CA, USA) was performed to determine free DNA in CSF and serum, as described previously [12].…”

From Stable to Lab—Investigating Key Factors for Sudden Deaths Caused by Streptococcus suis

“…Paraffin-embedded organs from Section 4.1 were cut into 4 µm sections and stretched on SuperFrost Plus™ adhesion slides (Thermo Fisher Scientific GmbH, Germany). Samples were deparaffinized and handled as previously described [68]. Briefly, the samples were incubated at room temperature for 1 h with primary antibodies diluted in blocking buffer.…”

Extracellular Traps: An Ancient Weapon of Multiple Kingdoms

“…This application did not alter the capacity of porcine neutrophils to release NETs or their MPO activity in response to PMA, ionomycin, or zymosan [67]. Interestingly, it has recently been shown that degraded neutrophil extracellular traps promote the growth of Actinobacillus pleuropneumoniae (A.pp) [130], an important porcine pathogen leading to high economic loss [131]. A.pp, itself, releases no nuclease, but the authors identified host nucleases as a source that degrades NETs after A.pp infection [130].…”

“…Interestingly, it has recently been shown that degraded neutrophil extracellular traps promote the growth of Actinobacillus pleuropneumoniae (A.pp) [130], an important porcine pathogen leading to high economic loss [131]. A.pp, itself, releases no nuclease, but the authors identified host nucleases as a source that degrades NETs after A.pp infection [130]. These data shed light on the detrimental effects of NETs during a host immune response against certain bacterial species that require or efficiently take advantage of degraded DNA material which has been provided by host nuclease or nucleases of other coinfecting bacteria as a source of growth-aiding nutrients.…”