Abstract
Granulocytes mediate the first line of defense against infectious diseases in humans as well as animals and they are well known as multitasking cells. They can mediate antimicrobial activity by different strategies depending on the pathogen they encounter. Besides phagocytosis, a key strategy against extracellular pathogens is the formation of extracellular traps (ETs). Those ETs mainly consist of DNA decorated with antimicrobial components and mediate entrapment of various pathogens. In the last years, various studies described ET formation as response to bacteria, viruses and parasites e.g., Trypanosma (T.) cruzi. Nevertheless, it is not fully understood, if ET formation helps the immune system to eliminate intracellular parasites. The goal of this study was to analyze ET formation in response to the intracellular parasite Trypanosma (T.) cruzi by granulocytes derived from animals that serve as natural reservoir. Thus, we investigated the ET formation in two T. cruzi reservoirs, namely dogs as domestic animal and common opossums (Didelphis marsupialis) as wild animal. Granulocytes were harvested from fresh blood by density gradient centrifugation and afterwards incubated with T. cruzi. We conducted the analysis by determination of free DNA and immunofluorescence microscopy. Using both methods, we show that T. cruzi efficiently induces ET formation in granulocytes derived from common opossum as well as dog blood. Most ETs from both animal species as response to T. cruzi are decorated with the protease neutrophil elastase. Since T. cruzi is well known to circulate over years in both analyzed animals as reservoirs, it may be assumed that T. cruzi efficiently evades ET-mediated killing in those animals. Therefore, ETs may not play a major role in efficient elimination of the pathogen from the blood of dogs or common opossums as T. cruzi survives in niches of their body. The characterization of granulocytes in various animals and humans may be helpful to understand the anti-pathogenic capacity and overall role of ETs against zoonotic pathogens like T. cruzi.
Highlights
The first line of defense against invading pathogens in humans and animals is formed by granulocytes that are able to rapidly infiltrate the infected tissue
In this study we aimed to investigate the formation of extracellular trap (ET) by granulocytes from dogs (Canis lupus familaris) and the common opossum (Didelphis (D.) marsupialis)
Three explanations are reasonable: Firstly, common opossums have in general more free DNA in the blood compared to dogs, as maybe the immune system is all the time in a steady state stadium of activation e.g., since they are all positive for T. cruzi Polymerase Chain Reaction (PCR)
Summary
The first line of defense against invading pathogens in humans and animals is formed by granulocytes that are able to rapidly infiltrate the infected tissue. These structures are mainly formed by neutrophil granulocytes and often named as neutrophil extracellular traps (NETs) (Brinkmann et al, 2004), but additional evidence is showing ET release by other granulocytes e.g., eosinophils as reviewed by Goldmann and Medina (2012) Those ETs or NETs consist of DNA and histones decorated with granule proteins as cell-type-specific proteases (e.g., elastase) (Urban et al, 2009) and cationic antimicrobial peptides (Neumann et al, 2014) that mediate extracellular entrapment and partial killing of microbes. Pre-treatment of parasites with NETs resulted in a significantly decreased number of parasites in the blood (SousaRocha et al, 2015)
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