Toll-like receptor (TLR)-3: a potent driving force behind rheumatoid arthritis

Toll-Like Receptor Signaling and Its Role in Cell-Mediated Immunity

Innate immunity is the first defense system against invading pathogens. Toll-like receptors (TLRs) are well-defined pattern recognition receptors responsible for pathogen recognition and induction of innate immune responses. Since their discovery, TLRs have revolutionized the field of immunology by filling the gap between the initial recognition of pathogens by innate immune cells and the activation of the adaptive immune response. TLRs critically link innate immunity to adaptive immunity by regulating the activation of antigen-presenting cells and key cytokines. Furthermore, recent studies also have shown that TLR signaling can directly regulate the T cell activation, growth, differentiation, development, and function under diverse physiological conditions. This review provides an overview of TLR signaling pathways and their regulators and discusses how TLR signaling, directly and indirectly, regulates cell-mediated immunity. In addition, we also discuss how TLR signaling is critically important in the host's defense against infectious diseases, autoimmune diseases, and cancer.

Toll-Like Receptor Signaling and Its Role in Cell-Mediated Immunity

Innate immunity is the first defense system against invading pathogens. Toll-like receptors (TLRs) are well-defined pattern recognition receptors responsible for pathogen recognition and induction of innate immune responses. Since their discovery, TLRs have revolutionized the field of immunology by filling the gap between the initial recognition of pathogens by innate immune cells and the activation of the adaptive immune response. TLRs critically link innate immunity to adaptive immunity by regulating the activation of antigen-presenting cells and key cytokines. Furthermore, recent studies also have shown that TLR signaling can directly regulate the T cell activation, growth, differentiation, development, and function under diverse physiological conditions. This review provides an overview of TLR signaling pathways and their regulators and discusses how TLR signaling, directly and indirectly, regulates cell-mediated immunity. In addition, we also discuss how TLR signaling is critically important in the host's defense against infectious diseases, autoimmune diseases, and cancer.

Innate immunity drives pathogenesis of rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease affecting ∼1% of the general population. This disease is characterized by persistent articular inflammation and joint damage driven by the proliferating synovial tissue fibroblasts as well as neutrophil, monocyte and lymphocyte trafficking into the synovium. The factors leading to RA pathogenesis remain poorly elucidated although genetic and environmental factors have been proposed to be the main contributors to RA. The majority of the early studies focused on the role of lymphocytes and adaptive immune responses in RA. However, in the past two decades, emerging studies showed that the innate immune system plays a critical role in the onset and progression of RA pathogenesis. Various innate immune cells including monocytes, macrophages and dendritic cells are involved in inflammatory responses seen in RA patients as well as in driving the activation of the adaptive immune system, which plays a major role in the later stages of the disease. Here we focus the discussion on the role of different innate immune cells and components in initiation and progression of RA. New therapeutic approaches targeting different inflammatory pathways and innate immune cells will be highlighted here. Recent emergence and the significant roles of innate lymphoid cells and inflammasomes will be also discussed.

The expression profile of toll-like receptor signaling molecules in CD19(+) B cells from patients with primary immune thrombocytopenia

BACKGROUND

B cells play a critical role in the pathogenesis of immune thrombocytopenia (ITP), and toll-like receptor (TLR) signaling is essential for the activation of autoreactive B cells. The objective of this study was to investigate the expression profile of TLR signaling molecules in circulating and splenic CD19(+) B cells isolated from ITP patients.

METHODS

CD19(+) B cells were magnetically isolated from peripheral blood and splenocytes. Human Toll-Like Receptor Signaling Pathway RT(2) Profiler™ PCR Array was used to determine the differences in mRNA expression of 84 TLR signaling pathway genes between ITP patients and controls. Flow cytometry was used to investigate intracellular expression of cytokines (IL-1β and IL-10).

RESULTS

A total of 31 genes involving TLR signaling pathways were differentially transcribed in circulating CD19(+) B cells, among which 27 were up-regulated in ITP. By comparison, differentially transcribed genes amounted to 39 in splenic B cells in ITP, among which only two were down-regulated. Up to 18 TLR signaling molecules exhibited up-regulated transcriptional levels both in splenic B cells and in circulating B cells in ITP. However, Only IL-10 and IL-1β were significantly upregulated in both the circulating and splenic B cells of patients with ITP. Intracellular staining of IL-10 and IL-1β confirmed the results of PCR Array.

CONCLUSIONS

The expression of TLRs and downstream cytokines, including IL-10 and IL-1β, is up-regulated in circulating and splenic B cells in ITP patients, suggesting that activated TLR signaling pathways in B cells may play dual roles in the pathophysiology of primary ITP.