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Bovine Respiratory Disease (BRD) is the primary cause of morbidity in the U.S. beef and dairy industries. BRD is caused by viral and bacterial agents that lead to severe pleuropneumonia in cattle, which is characterized by inflammation, intense neutrophil infiltration, consolidation and recently, extensive amounts of extracellular DNA in the lungs. One possible source of this DNA is from leukocytes that release fibrillar network referred to as extracellular traps (ETs). Previously, it was demonstrated that neutrophils and macrophages produce ETs in response to Mannheimia haemolytica and its leukotoxin (LKT). Conditioned media removed from bovine herpes virus (BHV)-infected bovine bronchiole epithelial (BBE) cells contained several cytokines including interferons, IL-1 and IL-6. Therefore, we examine if conditioned media from BBE cells infected with BHV affect ET formation from bovine neutrophils or macrophages. BBE cells were incubated with BHV for various times and conditioned media was removed and stored for further use. Leukocytes were co-incubated with conditioned media and M. haemolytica cells or its LKT for various amounts of time and ET formation was measured using PicoGreen fluorescence. Our data reveal a decrease in ET formation when conditioned media was co-incubated with macrophages and M. haemolytica cells or LKT in comparison to the control. However, neutrophils were unaffected by the co-incubation. Our findings suggest that BHV infection may cause a decrease in M. haemolytica- or LKT-induced ET formation, which could alter host defense and inflammation.

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Nicole Aulik



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