Respiratory Syncytial Virus Infection of Neonatal Monocytes Stimulates Synthesis of Interferon Regulatory Factor 1 and Interleukin-1β (IL-1β)-Converting Enzyme and Secretion of IL-1β

Abstract

Interleukin-1β (IL-1β) production in response to respiratory syncytial virus (RSV) was investigated in normal neonate monocytes. Intracellular or culture supernatant IL-1β protein levels were measured by enzyme immunoassay. The expression of mRNAs for interferon regulatory factor 1 (IRF-1), IL-1β-converting enzyme (ICE), and IL-1β in the cells was analyzed semiquantitatively by reverse transcriptase-PCR. Before RSV exposure, some IRF-1, ICE, and IL-1β transcripts were already expressed in the monocytes. The levels of these transcripts increased significantly 2 h after RSV exposure compared with those in mock-infected cells. At that time, significantly higher intracellular IL-1β protein levels were observed in RSV-exposed cells. After 20 h of RSV exposure, quantities of soluble IL-1β secreted from RSV-exposed cells were moderately higher than those from noninfected cells. These observations suggest that RSV infection of neonatal monocytes triggers enhanced transcription and increased translation of the IL-1β gene and increased secretion of the soluble protein. The later phase of these processes may be promoted by ICE activity, which was upregulated by increased IRF-1. The increase in IRF-1 activity may also result from RSV infection.