Carbohydrate-mediated interactions between chloroviruses and the immune system

Understanding the molecular mechanisms which drive and modulate host-pathogen interactions are essential when designing effective therapeutic and diagnostic approaches aimed at controlling infectious diseases. Certain large and giant viruses have recently been discovered as components of the human virome, yet little is known about their interactions with the host immune system. We have dissected the role of viral N-linked glycans during the interaction between the glycoproteins from six chloroviruses (belonging to three chlorovirus classes: NC64A, SAG, and Osy viruses) and the representative carbohydrate-binding receptors of the innate immune system. Using solid-phase assays we have identified the binding of viral glycoproteins to different C-type lectins in a carbohydrate-dependent manner. These experiments verified the importance of D-rhamnose in modulating their binding to C-type lectins DC-SIGN and Langerin. In vitro assays further determined the ability of the chlorovirus glycoproteins to trigger secretion of cytokines Interleukins 6 and 10 (IL-6 and IL-10) in human monocyte-derived dendritic cells and mouse macrophages. Additionally, IgG from healthy human controls recognized certain chlorovirus glycoproteins, indicating the significance of human environmental viral exposures. Collectively, these results demonstrate the ability of the innate and adaptive immune systems to recognize chlorovirus glycoproteins, a process dependent on their specific N-glycan structures.