Systemic Sclerosis is a complex autoimmune disease characterized by immune abnormalities, vascular damage, and fibrosis involving the skin and lungs. The host innate immune system plays a primary role in monitoring the containment of pathogens, and there is evidence of higher susceptibility to various types of infections in patients with autoimmune diseases. Recently, we found that Epstein-Barr virus (EBV) is deregulated in SSc with abnormal expression of viral lytic-genes in peripheral blood mononuclear cells (PBMCs), suggesting that the lytic form of EBV infection is poorly controlled in these patients. While EBV has long been proposed as a common factor for developing autoimmune and inflammatory reactions, the mechanism by which EBV contributes to the pathological processes is still unclear. In our lab we demonstrated the expression of EBV viral mRNA and lytic-proteins, which was also associated with aberrant antibody response against EBV lytic antigens, in the majority of fibroblasts and endothelial cells in SSc patients. Furthermore, we found that EBV elevates the expression of TLR7/9 and their downstream mediator mRNAs in infected fibroblasts, suggesting that EBV infection plays a role in inducing fibroblast innate immune responses. The evidence of EBV active infection raises the compelling question whether the lytic form of EBV could be detected by the cells of the innate immune system. In this regard, monocytes are an attractive population to be investigated, since these cells are involved in the innate immune control of viral replication and produce abundant amounts of IFN-I and other pro-inflammatory cytokines. Our preliminary studies revealed that the TLR8-molecular pathway is induced by EBV/lytic-genes in human monocytes, while it is not induced in latently infected cells. In this project we propose to further investigate EBV lytic infection as a mechanism contributing to autoimmunity through the activation of monocytes.
We believe that this proposal is highly innovative based on the following reasons:
1. The proposed studies will address a novel concept that innate immune dysregulation may be directly linked to an ongoing viral infection in autoimmune diseases. The presence of aberrant EBV reactivation in monocytes substantiates this important potential link in SSc.
2. Another novel finding of these studies is that EBV induces toll-like receptor 8 (TLR8) expression during viral replication in monocytes, while SSc monocytes spontaneously express elevated levels of TLR8. The relevance of this novel observation lies in the fact that TLR8 together with TLR7 are expressed on the X chromosome, which may help to explain the high prevalence of SSc, as well as other autoimmune diseases, in females.
3. This investigation will be the first to determine whether dysfunctional innate immune activation represents a trigger that induces EBV reactivation.
4. One of the most exciting aspects of this proposal is that we have identified for the first time that EBV replicates in monocytes of patients with SSc.
5. An important key technological innovation of the proposal is that we have successfully performed EBV lytic infection in THP1 cell lines generated from acute monocytic leukemia.