Role of toll-like receptor 4 and caspase-3, -8, and -9 in lipopolysaccharide-induced delay of apoptosis in equine neutrophils

OBJECTIVE To evaluate the effect of lipopolysaccharide (LPS) on apoptosis of equine neutrophils in vitro. SAMPLE Venous blood samples from 40 adult horses. PROCEDURES Neutrophils were isolated from blood samples and cultured with or without LPS from Escherichia coli O55:B5 for 12 or 24 hours. Neutrophil apoptosis was assessed by use of cytologic examination, annexin V and propidium iodide staining quantified with flow cytometry, coincubation with inducers of intrinsic and extrinsic apoptosis or a toll-like receptor (TLR) 4 inhibitor, and measurement of caspase-3, -8, and -9 activities. RESULTS Treatment with LPS resulted in a significant delay in apoptosis after incubation for 12 and 24 hours (neutrophils from blood samples of 40 horses). There was a significant correlation between increases in LPS dose and decreases in apoptosis after incubation for 24 hours (3 experiments, each of which involved neutrophils obtained from the same 3 horses at 3 separate times). Caspase-9 activity, but not caspase-3 or -8...