3.5 UVB-induced antigen-specific Tregs influence the clinical outcomes
To confirm the role of UVB-induced antigen-specific Tregs in disease modulation, we performed adoptive transfer experiments. Live GFP+ Tregs were sorted from the skin-draining LNs of Foxp3DTR-GFP mice under conditions of OVA-induced skin inflammation (Figure 4C and Figure S5A). Naive CD4+CD25-GFP- T cells (naive T cells) were sorted from OT-II/Foxp3DTR-GFP mice. A 1:1 mixture of Tregs and naive T cells was intravenously injected into recipient mice one day before sensitization with OVA/Alum followed by OVA patch challenges (Figure 4C). OVA-stimulated mice receiving naive T cells demonstrated significant skin inflammation and an influx of IL-5-producing CD4+ T cells into the skin. Neither Tregs from UVB-irradiated mice without OVA stimulation (UTregs) nor Tregs from OVA-stimulated mice without UVB treatment (OTregs) were able to prevent OVA-induced skin inflammation in recipient mice. However, Tregs from OVA-stimulated mice treated with UVB (O+UTregs) significantly mitigated these inflammatory responses (Figure 4D-F).
In mouse model of imiquimod (IMQ)-induced psoriasiform dermatitis, Tregs were intravenously administered to recipient mice one day before topical application of IMQ to the ears (Figure 4G). We found that neither UTregs, OTregs, nor O+UTregs could suppress the inflammation of skin infiltrated with IL-17- and IL-22-producing CD4+ T cells (Figure 4H,I) These findings demonstrate that UVB-induced antigen-specific Tregs are critical for clinical phenotypes of skin inflammatory diseases.
We further performed in vitro suppression assays to investigate the functional properties of these Treg populations. Bone marrow-derived dendritic cells (BMDCs) were generated from C57BL/6 mice and stimulated with LPS and OVA. UTregs, OTregs, and O+UTregs were assessed for their ability to inhibit BMDC activation and T-cell proliferation. ( Figure S5B). All three Treg populations exhibited comparable inhibitory effects on LPS-induced BMDC activation. However, O+UTregs demonstrated a stronger ability to suppress BMDC activation in the presence of OVA ( Figure S5C,D). Similarly, O+UTregs showed a higher ability to suppress the proliferation of naive OT-II T cells stimulated by OVA-pulsed BMDCs ( Figure S5E).