PD-L1 on mast cells suppresses effector CD8+ T-cell activation in the skin in murine contact hypersensitivity

• Published in: Journal of allergy and clinical immunology 2021-08, Vol.148 (2), p.563-573.e7
• Main Authors: Hirano, Tomoko, Honda, Tetsuya, Kanameishi, Shuto, Honda, Yuki, Egawa, Gyohei, Kitoh, Akihiko, Nakajima, Saeko, Otsuka, Atsushi, Nomura, Takashi, Dainichi, Teruki, Yaguchi, Tomonori, Inozume, Takashi, Kataoka, Tatsuki R., Tamada, Koji, Kabashima, Kenji
• Format: Article
• Language: English
• Subjects: Antibodies; Antigens; Apoptosis; Blocking antibodies; Bone marrow; CD8 antigen; Cell activation; Cell death; Contact dermatitis; Contact hypersensitivity; Cytokines; Dermatitis; Ear; Effector cells; Flow cytometry; Hypersensitivity; Laboratories; Lymphocytes; Lymphocytes T; mast cell; Mast cells; Melanoma; PD-1; PD-1 protein; PD-L1; PD-L1 protein; Peptides; Regulation; Skin diseases; Software; γ-Interferon
• ISSN: 0091-6749; 1097-6825
• DOI: 10.1016/j.jaci.2020.12.654

The programmed cell death-1 (PD-1)/programmed death ligand 1 (PD-L1) pathway is known to inhibit the activation of effector CD8+ T cells. However, just how this regulatory pathway is involved in the pathophysiology of CD8+ T-cell–mediated inflammatory skin diseases remains unclear. Our aim was to elucidate the mechanisms by which the PD-1/PD-L1 pathway exerts its regulatory roles in CD8+ T-cell–mediated cutaneous immune responses. PD-L1–deficient (Pdl1–/–) mice were used for the murine contact hypersensitivity model. Inflammatory responses such as IFN-γ production from CD8+ T cells in the skin was evaluated by flow cytometry. Compared with wild-type mice, Pdl1–/– mice exhibited exacerbated ear swelling and increased numbers of IFN-γ+ CD8+ T cells in the skin. Adoptive T-cell transfer experiments revealed the involvement of the PD-1/PD-L1 pathway in the elicitation phase of contact hypersensitivity. Bone marrow chimera experiments showed that PD-L1 on radioresistant cells was responsible for this regulatory pathway. Flow cytometric analysis revealed that among the radioresistant cells in the skin, PD-L1 was most highly expressed on mast cells (MCs) before and after elicitation. Administration of anti–PD-L1 blocking antibody during the elicitation phase significantly enhanced ear swelling responses and increased the number of IFN-γ+CD8+ T cells in the skin of wild-type mice, whereas no significant effects were observed in MC-deficient (WBB6F1/J-KitW/KitW-v/J and C57BL/6-KitW-sh/W-sh) mice. The high level of expression of PD-L1 on human skin MCs was confirmed by database analysis and immunohistochemical analysis. PD-L1 on MCs negatively regulates CD8+ T-cell activation in the skin. [Display omitted]