Differential expression of cytokine transcripts in neonatal and adult ovine alveolar macrophages in response to respiratory syncytial virus or toll-like receptor ligation

Abstract

Alveolar macrophages (AMϕs) secrete regulatory molecules that are believed to be critical in maintaining normal lung homeostasis. However, in response to activating signals, AMϕs have been shown to become to highly phagocytic cells capable of secreting significant levels of pro-inflammatory cytokines. There is evidence to suggest that susceptibility of Mϕ subpopulations to viral infection, and their subsequent cytokine/chemokine response, is dependent on age of the host. In the present study, we compared bovine respiratory syncytial virus (BRSV) replication and induction of cytokine responses in neonatal ovine AMϕs to those cells from isolated adult animals. While neonatal AMϕs could be infected with BRSV, viral replication was limited as previously shown for AMϕs from mature animals. Interestingly, following BRSV infection, peak mRNA levels of IL-1β and IL-8 in neonatal AMϕ were several fold higher than levels induced in adult AMϕs. In addition, peak mRNA expression for the cytokines examined occurred at earlier time points in neonatal AMϕs compared to adult AMϕs. However, the data indicated that viral replication was not required for the induction of specific cytokines in either neonatal or adult AMϕs. TLR3 and TLR4 agonists induced significantly higher levels of cytokine transcripts than BRSV in both neonatal and adult AMϕs. It was recently proposed that immaturity of the neonatal immune system extends from production of pro-inflammatory cytokines to regulation of such responses. Differential regulation of cytokines in neonatal AMϕs compared to adult AMϕs in response to RSV could be a contributory factor to more severe clinical episodes seen in neonates.

Innate Immunity to Respiratory Infection in Early Life

“…Stimulation of cultured cells has been used to interrogate the relative antimicrobial functions of neonatal and adult AMs. LPS stimulation of rodent or ovine AMs results in similar or even enhanced upregulation of TNF-α and CXC-chemokines in neonatal compared to adult cells (75)(76)(77), though others demonstrated a reduced translocation of NF-κB to the nucleus of AM from neonatal mice (78). Enhanced phagocytosis by neonatal compared to adult rat AM has been observed (75), but others have reported impaired phagocytosis and subsequent killing of yeast particles in neonatal rhesus monkey AMs; and impaired phagocytosis of opsonized red blood cells in neonatal rat AMs in comparison to adults (79,80).…”

Perinatal Lamb Model of Respiratory Syncytial Virus (RSV) Infection

“…Pulmonary dendritic cells isolated from term lamb lung differ from those isolated from adult lung in terms of antigen expression and maturation [75]. Ovine pulmonary dendritic cells from term lung support bRSV replication and have enhanced interleukin (IL)-4 and IL-10 gene transcripts [76,77].…”

Lentiviral vectors containing mouse Csf1r control elements direct macrophage-restricted expression in multiple species of birds and mammals

“…Sheep alveolar macrophages were isolated as per ref. 43 and cultured in Roswell Park Memorial Institute medium containing 20% sheep serum containing 10 4 U/ml (100 ng/ml) rhCSF1.…”