Th17 Cells in Autoimmune and Infectious Diseases

Abstract

The view of CD4 T-cell-mediated immunity as a balance between distinct lineages of Th1 and Th2 cells has changed dramatically. Identification of the IL-17 family of cytokines and of the fact that IL-23 mediates the expansion of IL-17-producing T cells uncovered a new subset of Th cells designated Th17 cells, which have emerged as a third independent T-cell subset that may play an essential role in protection against certain extracellular pathogens. Moreover, Th17 cells have been extensively analyzed because of their strong association with inflammatory disorders and autoimmune diseases. Also, they appear to be critical for controlling these disorders. Similar to Th1 and Th2 cells, Th17 cells require specific cytokines and transcription factors for their differentiation. Th17 cells have been characterized as one of the major pathogenic Th cell populations underlying the development of many autoimmune diseases, and they are enhanced and stabilized by IL-23. The characteristics of Th17 cells, cytokines, and their sources, as well as their role in infectious and autoimmune diseases, are discussed in this review.

Inflammasome Activation by ATP Enhances Citrobacter rodentium Clearance through ROS Generation

“…IL-6 is required for differentiation of naïve T cells into Th cells and TNF-α is a major product of Th cells; therefore, this observation is important in understanding the role of macrophages and bacterial killing during chronic infections. [30] As Crohn disease is known to be a Th-mediated inflammatory condition, the dysregulation (or dysfunction) of the inflammasome could lead to increased concentration of IL-6 and TNF-α, resulting in infiltration of Th cells into the lamina propria and more inflammation. This could be the consequence of impaired bacterial killing, as ATP appeared to reduce pro-inflammatory cytokines in our study [31].…”

A Review of Autoimmune Disease Hypotheses with Introduction of the “Nucleolus” Hypothesis

“…There is a balance maintained between Th1 and Th2 effects, but dysregulation can result in diseases. More recently, balance among Th17 cell subsets have come under suspicion since they control self-reactive T-cell proliferation [42][43][44][45][46] Skewed X inactivation One of the two X chromosomes in female cells may have genetic abnormalities or the X inactivation process cannot be established or maintained with the result that there is expression of abnormal X-linked proteins or abnormal protein levels due to improper X-linked dosage compensation that leads to an autoimmune response [51,53,54] Molecular mimicry Viral proteins or molecules in the diet that provoke an immune reaction could have epitopes similar to endogenous material. The immune reaction then spreads to an autoimmune reaction targeting the endogenous material.…”

“…The TH17 hypothesis (reviewed in [43][44][45]) is an update to the older Th1/Th2 balance hypothesis. Th17 cells are a subset of the CD4+ T cells that assist in removing extracellular pathogens.…”

Increased Proportion of Tc17 and Th17 Cells and Their Significant Reduction after Thymectomy May Be Related to Disease Progression in Myasthenia Gravis

“…These cells secrete different cytokines (IL-17A, IL-17F, IL-21, and IL-22), and their development and differentiation require specific transcription factors such as the retinoic acid receptor-related orphan receptor γ (RORγt) [13]. Studies have also indicated that CD8+ T cells have functions that extend beyond antigen-specific cell cytotoxicity.…”