Dendritic cells are functionally heterogeneous. How subsets interpret endogenous danger signals remains unclear.

Mitochondrial stress releases oxidized mitochondrial DNA (Ox-mtDNA) into circulation. Ox-mtDNA accumulates in autoimmune diseases, such as systemic lupus erythematosus. Yet its impact on dendritic cell function is unknown.

Here, we show that Ox-mtDNA selectively reprograms plasmacytoid dendritic cells (pDCs), but not conventional dendritic cells (cDCs). Both subsets internalized mtDNA. Strikingly, only pDCs engaged an NLRP3-dependent, autocrine IL-1β pathway in response to Ox-mtDNA.

This pathway induced co-stimulatory molecules and IL-21. It enabled pDCs to efficiently drive naïve CD4⁺ T cells into functional T follicular helper (Tfh) cells. Although pDCs produced robust interferon-α, this process did not require CD4⁺ T cell-intrinsic IFNAR signaling. In contrast, cDCs failed to support this Tfh differentiation program.

In vivo, sustained Ox-mtDNA release induced Tfh-dependent autoantibody production and glomerulonephritis. Blocking IL-1β signaling disrupted Tfh responses and antibody production.

Together, these findings identify Ox-mtDNA as a selective trigger of pDC function. They define a DC subset-specific pathway linking mitochondrial stress to adaptive immunity in autoimmunity. This axis provides a mechanistic basis for Tfh-driven disease and a tractable therapeutic target.