Human Properdin Released By Infiltrating Neutrophils Can Modulate Influenza A Virus Infection

Abstract

The complement system is designed to recognise and eliminate invading pathogens via activation of classical, alternative and lectin pathways. Human properdin stabilises the alternative pathway C3 convertase, resulting in an amplification loop that leads to the formation of C5 convertase, thereby acting as a positive regulator of the alternative pathway. It has been noted that human properdin on its own can operate as a pattern recognition receptor and exert immune functions outside its involvement in complement activation. Properdin can bind directly to microbial targets via DNA, sulfatides and glycosaminoglycans, apoptotic cells, nanoparticles, and well-known viral virulence factors. This study was aimed at investigating the complement-independent role of properdin against Influenza A virus infection. As one of the first immune cells to arrive at the site of IAV infection, we show here that IAV challenged neutrophils released properdin in a time-dependent manner. Properdin was found to directly interact with haemagglutinin, neuraminidase and matrix 1 protein Influenza A virus proteins in ELISA and western blot. Furthermore, modelling studies revealed that properdin could bind HA and NA of the H1N1 subtype with higher affinity compared to that of H3N2 due to the presence of an HA cleavage site in H1N1. In an infection assay using A549 cells, properdin suppressed viral replication in pH1N1 subtype while promoting replication of H3N2 subtype, as revealed by qPCR analysis of M1 transcripts. Properdin treatment triggered an anti-inflammatory response in H1N1-challenged A549 cells and a pro-inflammatory response in H3N2-infected cells, as evident from differential mRNA expression of TNF-α, NF-κB, IFN-α, IFN-β, IL-6, IL-12 and RANTES. Properdin treatment also reduced luciferase reporter activity in MDCK cells transduced with H1N1 pseudotyped lentiviral particles; however, it was increased in the case of pseudotyped H3N2 particles. Collectively, we conclude that infiltrating neutrophils at the site of IAV infection can release properdin, which then acts as an entry inhibitor for pandemic H1N1 subtype while suppressing viral replication and inducing an anti-inflammatory response. H3N2 subtype can escape this immune restriction due to altered haemagglutinin and neuraminindase, leading to enhanced viral entry, replication and pro-inflammatory response. Thus, depending on the subtype, properdin can either limit or aggravate IAV infection in the host.

Human C1q Regulates Influenza A Virus Infection and Inflammatory Response via Its Globular Domain

“…These results are in accordance with the previously reported data using the other complement regulators. The regulators of the classical and alternative pathways, Properdin, C4BP and Factor H respectively, were also found to modulate IAV infection in a subtype specific manner, in a manner similar to C1q (47,77,100). After treatment of H1N1 particles with factor H, VCP, C4BP, or properdin, A549 cells showed a decrease in M1 expression.…”

“…The findings of this study highlight a possible common mechanism that is used by the complement regulatory proteins to modulate the IAV infection in a complement-independent manner. A recent in silico binding analysis between properdin and HA revealed that the binding sites of the top docked poses of properdin with HA of H1N1 and H3N2 were proximal [ 100 ]. However, properdin was found to interact with the HA cleavage site of H1N1, but not H3N2 (3).…”

Neutrophil-derived complement factor P induces cytotoxicity in basal-like cells via caspase 3/7 activation in pancreatic cancer

“…Studies suggest that N1 neutrophils may have potent anticancer effects through antibody-dependent or direct cytotoxicity, as well as ROS-mediated coupling (Hicks et al, 2006). Infiltrating neutrophils are known to locally secrete properdin, which is stored in their granules (Varghese et al, 2021). Properdin may recognize cancer cells and play a protective role during tumorigenesis, as suggested by some studies (Fuster and Esko, 2005; Sjöblom et al, 2006).…”

The Immunosuppressive Roles of PD-L1 during Influenza A Virus Infection

“…Influenza A virus (IAV) is a top global threat to public health, causing severe pneumonia. IAV infection motivates host innate immune responses, including expression of type-I and type-III interferons (IFNs), through manifold signal transduction pathways, such as pathogen recognition receptor-mediated signaling [1][2][3][4][5][6][7][8]. Upon the recognition of viral pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs), inflammatory cytokines, including interleukin-1β (IL-1β), IL-6, and tumor necrosis factor alpha, are produced in hosts in response to IAV infection [5,[9][10][11][12][13][14].…”

“…IAV infection motivates host innate immune responses, including expression of type-I and type-III interferons (IFNs), through manifold signal transduction pathways, such as pathogen recognition receptor-mediated signaling [1][2][3][4][5][6][7][8]. Upon the recognition of viral pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs), inflammatory cytokines, including interleukin-1β (IL-1β), IL-6, and tumor necrosis factor alpha, are produced in hosts in response to IAV infection [5,[9][10][11][12][13][14]. Although these cytokines play critical antiviral roles in the first line of host defense against IAV infection, excessive inflammatory responses to IAV infection can lead to viral pathogenesis [9,12].…”