Induction of functional defects in macrophages by a poult enteritis and mortality syndrome-associated turkey
M A Qureshi1, Y M Saif, C L Heggen-Peay
1Department of Poultry Science, North Carolina State University, Raleigh 27695-7608, USA.
Abstract:
The interaction of a poult enteritis and mortality syndrome (PEMS)-turkey astrovirus-Ohio State University (TAst-OSU) with the mononuclear phagocytic system cells, namely macrophages, was examined after in vitro and in vivo exposure. In vitro exposures were performed by incubating adherent turkey macrophages with various volumes of 10(6) 50% embryo infective dose (EID50)/ml TAst-OSU stock, whereas for in vivo challenge, poults were given a 200 microl inoculum of 10(6) EID50/ml TAst-OSU stock at 7 days of age. Results show that TAst-OSU in vitro exposure reduced macrophage viability relative to controls (P < 0.05) and decreased phagocytosis (P < 0.05) and intracytoplasmic killing of Escherichia coli (P < 0.05) after a 42-48-hr exposure. Poults challenged with TAst-OSU in vivo recruited almost 50% fewer Sephadex-elicited inflammatory cells in the abdominal cavity (P < 0.05) as compared with the sham controls. Similar to in vitro exposure, macrophages isolated from in vivo TAst-OSU-challenged poults exhibited reduced percentage of phagocytic macrophages (P < 0.05) as well as fewer intracytoplasmic E. coli per phagocytic macrophage (P < 0.05). TAst-OSU-challenged poults had a greater number of viable E. coli in their spleens (P < 0.05) after an intravenous E. coli challenge as compared with the non-TAst-OSU-challenged control poults. Macrophage-mediated cytokines and metabolites were also examined during this study. Both in vitro and in vivo TAst-OSU challenge resulted in reduced interleukin (IL)-1 and IL-6 activity. On the contrary, nitrite levels in macrophage culture supernatant fraction of TAst-OSU-challenged macrophages were significantly higher (P < or = 0.05). The findings of these studies indicated that TAst-OSU challenge induced defects in macrophage effector functions, implying that PEMS-turkey astrovirus can potentially impair the immune response of turkeys, thereby leading to enhanced susceptibility of turkeys to secondary, perhaps even fatal, bacterial infections.
Insights
Turkey astrovirus impairs macrophage function, reducing their ability to fight bacteria. This viral infection in poults can increase susceptibility to secondary bacterial infections.
Area of Science:
- Veterinary Virology
- Immunology
- Poultry Diseases
Background:
- Poult enteritis and mortality syndrome (PEMS) is a significant concern in turkey farming.
- Turkey astrovirus-Ohio State University (TAst-OSU) is implicated in PEMS.
- The impact of TAst-OSU on the innate immune system, specifically macrophages, requires further investigation.
Purpose of the Study:
- To investigate the interaction between TAst-OSU and turkey macrophages.
- To assess the effects of TAst-OSU on macrophage viability, phagocytosis, and bacterial killing.
- To evaluate the impact of TAst-OSU on the in vivo immune response and cytokine production in turkeys.
Main Methods:
- In vitro exposure of turkey macrophages to TAst-OSU.
- In vivo challenge of 7-day-old poults with TAst-OSU.
- Assessment of macrophage viability, phagocytosis of Escherichia coli, and intracellular killing.
- Analysis of inflammatory cell recruitment and cytokine (IL-1, IL-6) and nitrite levels.
- Evaluation of bacterial load in spleen after E. coli challenge.
Main Results:
- In vitro TAst-OSU exposure reduced macrophage viability, phagocytosis, and E. coli killing.
- In vivo TAst-OSU challenge decreased inflammatory cell recruitment and macrophage phagocytic activity.
- TAst-OSU-challenged poults showed increased E. coli in spleens post-challenge.
- Reduced IL-1 and IL-6 activity, but increased nitrite levels, were observed in TAst-OSU-exposed macrophages.
Conclusions:
- TAst-OSU infection induces significant defects in macrophage effector functions.
- These immune deficits may render turkeys more vulnerable to secondary bacterial infections.
- TAst-OSU poses a potential threat to turkey health by compromising the immune system.
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