Anti-PPIL-5 antibody exacerbates disease of severe influenza in a murine experimental model

Abstract Respiratory viruses such as SARS-CoV2 cause serious emerging infectious diseases. Even seasonal influenza results in significant morbidity and mortality. Host immunity responds to influenza virus infection to eradicate the pathogen. However, dysregulated responses such as the cytokine storm contribute to severe disease. Mechanistic dissection of immune regulation may offer practical solutions for severe influenza. In our mouse model of severe influenza, a LAG-3 regulatory response evolves with the pro-inflammatory IFN-γ response in influenza virus hemagglutinin (HA)-specific CD4+ T cells. Adoptive transfer of LAG-3(+) IFN-γ(-) HA-specific CD4+ T cells suppressed lung inflammation without compromised virus eradication. Genomic study of LAG-3(+) IFN-γ(−) CD4+ T cells revealed up-regulation of the PPIL-5 [Peptidylprolyl isomerase (Cyclophilin)-like 5] gene. PPIL-5(+) HA-specific CD4+ T cells accumulated in the lung with time after infection. PPIL-5 protein suppressed HA-specific CD4+ T cell activation in vitro in a dose dependent manner. PPIL-5 blockade in vitro with siRNA reversed immune suppression and unleashed activation of HA-specific CD4+ T cells. PPIL-5 blockade in vivo with monoclonal anti-PPIL-5 antibodies attenuated LAG-3 and PD-1 and augmented IFN-γ responses of the lung-infiltrating HA-specific CD4+ T cells, with aggravated disease and intensified mortality of severe influenza. The HA-specific CD4+ T cells took less glucose and produced lactate with anti-PPIL-5 blockade. They adopted anaerobic glycolysis in this reverted inflammatory response. Our results suggest that PPIL-5, similar to LAG-3, is also an immune checkpoint and a possible target to be manipulated for alleviation of severe influenza. The Research Center for Emerging Viral Infections receives support from The Featured Areas Research Center Program within the framework of the Higher Education Sprout Project by the Ministry of Education (MOE), Taiwan and NSTC 111-2634-F-182-001 from the National Science and Technology Council, Taiwan. This work was supported by Projects MOST 111-2314-B-182-029 (AD) and MOST-105-2321-B-182A-003-MY3 (AD) from the National Science and Technology Council, Taiwan, and by CMRPG3L1671 (CTH), CMRPVVJ0052 (CTH), and CMRPG3J1771 (CYH) from the Medical Research Project Fund, Chang Gung Memorial Hospital, Taiwan.