Strain Dependent Differences in Magnitude and Timing of Innate Immune Responses to Respiratory Syncytial Virus (RSV) in Human Monocyte Derived Dendritic Cells (MDDC)

Abstract

RATIONALE: RSV disease severity in infants may be determined by the infecting virus strain. Comparing RSV strains of different severity may identify immune mechanisms associated with severe disease and its sequelae. RSV line 19 elicits severe disease in mice characterized by enhanced mucous secretion and IL-13 expression, and low expression of IFN-alpha compared to mice infected with the laboratory strain A2. We examined the human innate immune response induced by RSV line 19 in comparison to strain A2.METHODS: qRT-PCR based methods were used to determine expression of inflammatory and interferon response genes (IRG). Type I and III IFN subtype gene expression was assessed using a novel PCR assay developed in our lab.RESULTS: Both RSV strains elicited similar expression patterns of IRG and inflammatory genes, but at 24 hours, the response to line 19 was attenuated. Similarly, at 24 hours, either strain elicited expression of IFN-alpha1, -alpha14, -beta, -lambda1 and -lambda2, but these were expressed as much as 200 fold lower in response to line 19. Reduced IFN protein in supernatants in response to line 19 at 24 hours reflected that pattern. In contrast, the pattern was reversed at 8 hours, such that line 19 elicited higher expression of IRGs and up to 130 fold higher expression of the same IFN subtypes.CONCLUSIONS: RSV elicits a specific type I and type III IFN signature in MDDC, however, the more severe line 19 induces a faster but ultimately attenuated innate immune response compared to the milder, but more commonly used A2 laboratory strain. RATIONALE: RSV disease severity in infants may be determined by the infecting virus strain. Comparing RSV strains of different severity may identify immune mechanisms associated with severe disease and its sequelae. RSV line 19 elicits severe disease in mice characterized by enhanced mucous secretion and IL-13 expression, and low expression of IFN-alpha compared to mice infected with the laboratory strain A2. We examined the human innate immune response induced by RSV line 19 in comparison to strain A2. METHODS: qRT-PCR based methods were used to determine expression of inflammatory and interferon response genes (IRG). Type I and III IFN subtype gene expression was assessed using a novel PCR assay developed in our lab. RESULTS: Both RSV strains elicited similar expression patterns of IRG and inflammatory genes, but at 24 hours, the response to line 19 was attenuated. Similarly, at 24 hours, either strain elicited expression of IFN-alpha1, -alpha14, -beta, -lambda1 and -lambda2, but these were expressed as much as 200 fold lower in response to line 19. Reduced IFN protein in supernatants in response to line 19 at 24 hours reflected that pattern. In contrast, the pattern was reversed at 8 hours, such that line 19 elicited higher expression of IRGs and up to 130 fold higher expression of the same IFN subtypes. CONCLUSIONS: RSV elicits a specific type I and type III IFN signature in MDDC, however, the more severe line 19 induces a faster but ultimately attenuated innate immune response compared to the milder, but more commonly used A2 laboratory strain.