Upregulation of PD-L1 Expression by Prostaglandin E2 and the Enhancement of IFN-γ by Anti-PD-L1 Antibody Combined With a COX-2 Inhibitor in Mycoplasma bovis Infection.

Shintaro Goto ,Motoshi Tajima,Kei Watari,Junko Kohara,Satoru Konnai,Hidetoshi Higuchi,Satoshi Gondaira,Kazuhiko Ohashi,Keiichi Yamamoto,Yasuhiko Suzuki,Tomohiro Okagawa,Yukinari Kato,Yuki Hirano,Atsuhi Kobayashi,Mika K Kaneko,Masateru Koiwa,Shinji Yamada,Erina Minato,Naoya Maekawa,Eiji Taguchi,Yamato Sajiki,Ryoko Uemura,Motoo Shiro ,Motomu Toda

doi:10.3389/fvets.2020.00012

Abstract

Bovine mycoplasmosis caused by Mycoplasma bovis results in pneumonia and mastitis in cattle. We previously demonstrated that the programmed death 1 (PD-1)/PD-ligand 1 (PD-L1) pathway is involved in immune dysfunction during M. bovis infection and that prostaglandin E2 (PGE2) suppressed immune responses and upregulated PD-L1 expression in Johne's disease, a bacterial infection in cattle. In this study, we investigated the role of PGE2 in immune dysfunction and the relationship between PGE2 and the PD-1/PD-L1 pathway in M. bovis infection. In vitro stimulation with M. bovis upregulated the expressions of PGE2 and PD-L1 presumably via Toll-like receptor 2 in bovine peripheral blood mononuclear cells (PBMCs). PGE2 levels of peripheral blood in infected cattle were significantly increased compared with those in uninfected cattle. Remarkably, plasma PGE2 levels were positively correlated with the proportions of PD-L1+ monocytes in M. bovis-infected cattle. Additionally, plasma PGE2 production in infected cattle was negatively correlated with M. bovis-specific interferon (IFN)-γ production from PBMCs. These results suggest that PGE2 could be one of the inducers of PD-L1 expression and could be involved in immunosuppression during M. bovis infection. In vitro blockade assays using anti-bovine PD-L1 antibody and a cyclooxygenase 2 inhibitor significantly upregulated the M. bovis-specific IFN-γ response. Our study findings might contribute to the development of novel therapeutic strategies for bovine mycoplasmosis that target PGE2 and the PD-1/PD-L1 pathway.

Highlights

Bovine mycoplasmosis caused by Mycoplasma bovis is characterized by chronic pneumonia, therapy-resistant mastitis, otitis, and arthritis [1,2,3,4]
To test whether culture supernatants containing PGE2 induced by M. bovis upregulated PD-ligand 1 (PD-L1) expression, peripheral blood mononuclear cells (PBMCs) from uninfected cattle were cultured in supernatant from PBMCs that were co-cultured with live M bovis for 24 h
PBMCs from uninfected cattle were incubated with PGE2 and PD-L1 expression on monocytes was analyzed by flow cytometry

Summary

Introduction

Bovine mycoplasmosis caused by Mycoplasma bovis is characterized by chronic pneumonia, therapy-resistant mastitis, otitis, and arthritis [1,2,3,4]. M. bovis has several immunosuppressive characteristics in vitro, such as inhibition of proliferative response of bovine peripheral blood mononuclear cells (PBMCs), induction of apoptosis in bovine lymphocytes, and delay of apoptosis in bovine monocytes, along with suppressed production of interferon (IFN)-γ and tumor necrosis factor (TNF)-α [5,6,7]. These characteristics could cause chronic progression of the disease and, especially during the lung infection, and allow coinfection with other bacteria and viruses [2, 3]. The T cell exhaustion caused by PD-1/PD-L1 might be involved in the immune dysfunction during bovine mycoplasma

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Conclusion