A106-05 Mechanism of Surfactant Protein-A (SP-A) Mediated Regulation of Toll-like Receptors (TLRS) in Respiratory Syncytial Virus (RSV) Pathogenesis

Background Surfactant protein A (SP-A) is a key regulator of pulmonary innate immunity. Human SP-A consists of two proteins, SP-A1 and SP-A2, encoded by the SFTPA1 and SFTPA2 genes, respectively. The SFTPA2-1A0 variant is the most prevalent (∼5%) and has been associated with increased severity of RSV infection in infants, although the underlying mechanisms remain poorly understood. Since SP-A modulates Toll-like receptor (TLR) signaling, which is central to antiviral responses, we hypothesized that SP-A variants may differentially influence TLR-mediated immune pathways during RSV infection. Objective We aim to investigate how native SP-A (nSP-A) and the SFTPA2-1A0 variant regulate endosomal TLR signaling in response to RSV infection. Methods A549 lung epithelial cells were mock-infected or infected with RSV A2 and pretreated with either nSP-A or the 1A0 variant protein. Samples were collected at 18, 24-, 48-, 72-, and 96-hours post-infection. Viral load (RSV NS1) and expression of TLR2, TLR3, TLR4, TLR7, and TLR9 were measured using RT-qPCR. Cytokines (TNF-α and IFN-β) were quantified by ELISA. Results RT-qPCR analysis revealed a time-dependent increase in RSV-NS1 expression (Figure1A). Both nSP-A and 1A0 reduced viral load compared to RSV-only cells, with nSP-A demonstrating more sustained suppression, particularly between 24-72 hours. RSV infection significantly upregulated TLR3 expression, peaking at 24 hours (Figure 1B). This induction was attenuated by nSP-A and only partially reduced by the 1A0 variant. No significant changes were observed in the expression of TLR2, TLR4, TLR7, or TLR9.ELISA showed that RSV infection elevated IFN-β levels (Figure 2). Both nSP-A and 1A0 treatments reduced IFN-β responses compared to RSV-only cells. TNF-α levels were undetectable in all samples. Conclusion SP-A and its genetic variant modulate the innate immune response to RSV by suppressing viral replication and TLR3 expression. However, the 1A0 variant exhibits a diminished ability to regulate these responses compared to nSP-A. These findings suggest that the association between the 1A0 variant and RSV severity may be due to its impaired capacity to mount a robust antiviral response through TLR3 pathway. Targeting this pathway may offer a potential therapeutic strategy. This abstract is funded by: NIH-NHLBI