Intrathymic Selection and Defects in the Thymic Epithelial Cell Development

Peripheral T-cell responses of EphB2- and EphB3-deficient mice in a model of collagen-induced arthritis

Both EphB2- and EphB3-deficient mice exhibit profound histological alterations in the thymic epithelial network but few changes in T-cell differentiation, suggesting that this organization would be sufficient to produce functional T lymphocytes. Also, other antigen-presenting cells involved in immunological education could substitute the thymic epithelium. Accordingly, we found an increased frequency of plasmacytoid dendritic cells but not of conventional dendritic cells, medullary fibroblasts or intrathymic B lymphocytes. In addition, there are no lymphoid infiltrates in the organs of mutant mice nor do they contain circulating autoantibodies. Furthermore, attempts to induce arthritic lesions after chicken type II collagen administration fail totally in EphB2-deficient mice whereas all WT and half of the immunized EphB3-/- mice develop a typical collagen-induced arthritis. Our results point out that Th17 cells, IL4-producing Th2 cells and regulatory T cells are key for the induction of disease, but mutant mice appear to have deficits in T cell activation or cell migration properties. EphB2-/- T cells show reduced in vitro proliferative responses to anti-CD3/anti-CD28 antibodies, produce low levels of anti-type II collagen antibodies, and exhibit low proportions of T follicular helper cells. On the contrary, EphB3-/- lymph node cells respond accurately to the different immune stimuli although in lower levels than WT cells but show a significantly reduced migration in in vitro transwell assays, suggesting that no sufficient type II collagen-dependent activated lymphoid cells reached the joints, resulting in reduced arthritic lesions.

Cytosolic Nuclear Sensor Dhx9 Controls Medullary Thymic Epithelial Cell Differentiation by p53-Mediated Pathways

Thymic epithelial cells (TECs) critically participate in T cell maturation and selection for the establishment of immunity to foreign antigens and immune tolerance to self-antigens of T cells. It is well known that many intracellular and extracellular molecules elegantly have mastered the development of medullary TECs (mTECs) and cortical TECs (cTECs). However, the role played by NTP-dependent helicase proteins in TEC development is currently unclear. Herein, we created mice with a TEC-specific DExD/H-box helicase 9 (Dhx9) deletion (Dhx9 cKO) to study the involvement of Dhx9 in TEC differentiation and function. We found that a Dhx9 deficiency in TECs caused a significant decreased cell number of TECs, including mTECs and thymic tuft cells, accompanied by accelerated mTEC maturation but no detectable effect on cTECs. Dhx9-deleted mTECs transcriptionally expressed poor tissue-restricted antigen profiles compared with WT mTECs. Importantly, Dhx9 cKO mice displayed an impaired thymopoiesis, poor thymic T cell output, and they suffered from spontaneous autoimmune disorders. RNA-seq analysis showed that the Dhx9 deficiency caused an upregulated DNA damage response pathway and Gadd45, Cdkn1a, Cdc25, Wee1, and Myt1 expression to induce cell cycle arrest in mTECs. In contrast, the p53-dependent upregulated RANK-NF-κB pathway axis accelerated the maturation of mTECs. Our results collectively indicated that Dhx9, a cytosolic nuclear sensor recognizing viral DNA or RNA, played an important role in mTEC development and function in mice.

Disruption of thymic central tolerance by infection with murine roseolovirus induces autoimmune gastritis

Infections with herpesviruses, including human roseoloviruses, have been proposed to cause autoimmune disease, but defining a causal relationship and mechanism has been difficult due to the ubiquitous nature of infection and development of autoimmunity long after acute infection. Murine roseolovirus (MRV) is highly related to human roseoloviruses. Herein we show that neonatal MRV infection induced autoimmune gastritis (AIG) in adult mice in the absence of ongoing infection. MRV-induced AIG was dependent on replication during the neonatal period and was CD4+ T cell and IL-17 dependent. Moreover, neonatal MRV infection was associated with development of a wide array of autoantibodies in adult mice. Finally, neonatal MRV infection reduced medullary thymic epithelial cell numbers, thymic dendritic cell numbers, and thymic expression of AIRE and tissue-restricted antigens, in addition to increasing thymocyte apoptosis at the stage of negative selection. These findings strongly suggest that infection with a roseolovirus early in life results in disruption of central tolerance and development of autoimmune disease.

Molecular and Cellular Basis of Autoimmune Diseases

The defense organization of our organism is found in the immune system, which has two important components, the innate and the adaptive immunity, where different molecules, cells, and organs are involved and coordinated to protect us from external and internal damage [...].