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Cross-tolerization tale
Conventional type 1 dendritic cells (cDC1s) present exogenous antigen on MHCI to CD8+ T cells through the process of cross-presentation. Wohn et al. now show that MHCII on cDC1s is required for cross-tolerization of CD8+ T cells. They developed a mouse model in which Cre recombinase is expressed under control of the cDC1 marker XC chemokine receptor (XCR1) to generate mice that are specifically lacking MHCII on cDC1 cells. MHCII-deficient cDC1s could not cross-tolerize autoreactive CD8+ T cells but instead converted them into effector CD8+ T cells that caused a lethal autoimmune response. The ability of cDC1s to enforce cross-tolerization is not completely acquired during homeostatic maturation but requires MHCII-restricted interactions with regulatory T cells.
Abstract
Conventional dendritic cells expressing the XCR1 chemokine receptor (cDC1s) excel at cross-presentation. Here, we developed and used a mouse model in which a Cre recombinase is expressed under the control of the Xcr1 gene while preserving XCR1 expression. We used it to generate mice with conditional deletion of MHC class II (MHCII) molecules on cDC1s. By preventing cDC1s to receive suppressive regulatory T cell inputs via MHCII-restricted interactions, the objective of the present study was to gauge whether MHCII-deficient cDC1s lose their capacity of tolerizing autoreactive CD8+ T cells. Whereas MHCII+ cDC1 readily cross-tolerized strongly autoreactive CD8+ T cells specific for a keratinocyte-derived self-antigen, MHCII-deficient cDC1s converted them into potent effectors capable of triggering a fast-onset lethal autoimmunity associated with severe skin histopathological manifestations. Preventing egress of such pathogenic self-reactive CD8+ T cell effectors from the cutaneous draining lymph nodes abrogated the autoimmune condition. Therefore, our results revealed that the cross-tolerizing capacity of cDC1s is not a property fully acquired at the time they undergo homeostatic maturation but needs to be enforced via MHCII-restricted, suppressive interactions with regulatory T cells.
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