Virus-like particle surface toll-like receptor signaling modulates host response to bacterial infection

Abstract

Innate immune recognition of viruses is critical for the rapid response and subsequent clearance of an infection. The primary focus of virus innate immune recognition is the recognition of viral nucleic acids post-infection. However, innate pattern recognition receptors (PRRs) have been demonstrated to recognize viral proteins independent of infection. One group of PRRs associated with viral recognition are Toll-like Receptors (TLRs). With the discovery of TLRs in the late 1990's, over two decades of research have endeavored to identify if cell surface TLRs recognize viral proteins and if so, understand whether surface TLR-viral recognition benefits the host or the virus. To the benefit of the host, it was previously determined that host-recognition of viral proteins protects mice from bacterial infection early post-virus exposure, independent of viral nucleic acids (virus-like particle; VLP). This suggested that early viral protein recognition could protectively prime the host against bacterial infection. Our investigation here attempts to address the generality of surface TLR-virus recognition independent of infection, how viral protein recognition alters the subsequent signaling response to bacterial infection, and finally, if/how expression system-associated variables interfere with the interpretation of our study. We utilized macrophage deficient in surface TLRs and TLR-associated signaling proteins to address the TLR signaling pathway responsible for the general response to VLPs that results in reduced bacterial burden. We found that different surface TLRs were responsible for reducing bacterial burden, resulting in the activation of different signaling pathways dependent upon the VLP macrophages were exposed to. In addition, our results demonstrate how expression system-associated variables alter the interpretation of signaling pathways activated by surface TLRs.