Respiratory syncytial virus inhibits granulocyte apoptosis through a phosphatidylinositol 3-kinase and NF-kappaB-dependent mechanism

Respiratory syncytial virus (RSV) is a common cause of lower respiratory tract disease in children. It is associated with increased neutrophil numbers in the airway. In this study, we assessed whether this ssRNA virus can directly influence granulocyte longevity. By culturing RSV with granulocytes,...

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Bibliographic Details
Published in:The Journal of immunology (1950) 2006-05, Vol.176 (9), p.5529-5537
Main Authors: Lindemans, Caroline A, Coffer, Paul J, Schellens, Ingrid M M, de Graaff, Patricia M A, Kimpen, Jan L L, Koenderman, Leo
Format: Article
Language:English
Subjects:
Apoptosis
Cells, Cultured
Endosomes - metabolism
Gene Expression Regulation
Granulocytes - cytology
Granulocytes - metabolism
Humans
Interleukin-6 - biosynthesis
Myeloid Cell Leukemia Sequence 1 Protein
Neoplasm Proteins - metabolism
NF-kappa B - metabolism
Phosphatidylinositol 3-Kinases - metabolism
Proto-Oncogene Proteins c-bcl-2 - metabolism
Respiratory Syncytial Viruses - physiology
Toll-Like Receptor 4 - metabolism
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Summary:Respiratory syncytial virus (RSV) is a common cause of lower respiratory tract disease in children. It is associated with increased neutrophil numbers in the airway. In this study, we assessed whether this ssRNA virus can directly influence granulocyte longevity. By culturing RSV with granulocytes, it was observed that virus delays both constitutive neutrophil and eosinophil apoptosis. Using pharmacological inhibitors, the RSV-induced delay in neutrophil apoptosis was found to be dependent on both PI3K and NF-kappaB, but not p38 MAPK or MEK1/MEK2 activation. Using blocking Abs and a reporter cell line, we were able to exclude TLR4 as the receptor responsible for mediating RSV-induced delay in neutrophil apoptosis. The antiapoptotic effect was abrogated by preincubation with the lysosomotropic agent chloroquine, indicating the requirement for endolysosomal internalization. Furthermore, addition of ssRNA, a ligand for the intracellular TLR7/TLR8, also inhibited neutrophil apoptosis, suggesting that intracellular TLRs could be involved in induction of the antiapoptotic effect. Using the BioPlex cytokine detection assay (Bio-Rad), we found that IL-6 was present in supernatants from RSV-exposed neutrophils. IL-6 was found to inhibit neutrophil apoptosis, suggesting that there is an autocrine or paracrine antiapoptotic role for IL-6. Finally, RSV treatment of neutrophils resulted in increased expression of the antiapoptotic Bcl-2 protein Mcl-1. Taken together, our findings suggest involvement of multiple intracellular mechanisms responsible for RSV-induced survival of granulocytes and point toward a role for intracellular TLRs in mediating these effects.
ISSN:0022-1767