The autoimmune regulator Aire is expressed in a small proportion of medullary thymic epithelial cells (mTECs) and is crucial in the induction of central T cell tolerance. The origin and development of Aire(+) mTECs, however, are not well understood. Here we demonstrate that the tight-junction components claudin-3 and claudin-4 (Cld3,4) were 'preferentially' expressed in Aire(+) mTECs. In early ontogeny, Cld3,4(hi) TECs derived from the most apical layer of the stratified thymic anlage first expressed known mTEC markers such as UEA-1 ligand and MTS10. We provide evidence that such Cld3,4(hi) UEA-1(+) TECs represented the initial progenitors specified for Aire(+) mTECs, whose development crucially required NF-kappaB-inducing kinase and the adaptor molecule TRAF6. Our results suggest that Aire(+) mTECs represent terminally differentiated cells in a unique lineage arising during thymic organogenesis.

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Immune aging results in diminished adaptive immunity and increased risk for autoimmunity. We previously reported a unique PD-1+ CD44highCD4+ T cell population that increases with age in normal mice. In this study, we indicate that the age-dependent PD-1+ CD44highCD4+ T cells develop as unique T follicular (TF) cells in a B cell–dependent manner and consist of two subpopulations, as follows: CD153+ cells preferentially secreting abundant osteopontin on TCR stimulation and CD153− cells that are apparently TCR anergic. These unique TF cells with essentially similar features increase much earlier and are accumulated in the spontaneous germinal centers (GCs) in lupus-prone female BWF1 (f-BWF1) mice. These TF cells showed characteristic cell-senescence features and developed in association with extensive CD4+ T cell proliferation in vivo, suggesting replicative senescence. Although the CD153+ TF cells were defective in proliferation capacity, they were quite stable and specifically responded to self GC-B cells to secret abundant osteopontin, which inhibited B cell receptor–induced GC-B cell apoptosis in f-BWF1 mice. Transfer of CD153+ PD-1+ CD4+ T cells promoted the growth of spontaneous GCs, whereas administration of anti-osteopontin Ab suppressed GC enlargement and anti-nuclear Ab production and ameliorated clinical lupus nephritis of f-BWF1 mice. Current results suggest that senescent CD153+ TF cells generated as a consequence of extensive endogenous CD4+ T cell proliferation play an essential, if not sufficient, role in lupus pathogenesis in lupus-prone genetic background and may also contribute to an increased autoimmunity risk with age.

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