PD-1 expression on immune cells in sepsis mouse model and the susceptibility to secondary fungal infection

Abstract

Objectives: This study aimed to i) determine the kinetic changes of immune cell phenotypes, including an exhaustion marker PD-1, in spleens of murine sepsis ii) investigate the susceptibility against secondary fungal infection after sepsis, and iii) investigate the efficacy of an anti-PD-1 treatment in post-sepsis fungal infection.

Methods: Cecal ligation and puncture (CLP) was used as a sepsis model and splenocytes post-CLP were assessed by flow cytometry. In addition, secondary post sepsis systemic fungal infections by Candida albicans or Aspergillus fumigatus administration at 5-day post-CLP were performed. Moreover, secondary aspergillosis was treated with Amphotericin B with or without anti-PD-1 to explore anti-PD-1 effectiveness.

Results: T cells and B cells, but not macrophages, in mouse spleens were decreased post-CLP. Increased expression of PD-1 (immune exhaustion marker) on T cell and B cell was demonstrated at 5 and 12 days post-CLP. In parallel, PD-1 expression on macrophage was increased at 1 day post-CLP and decreased at 12 days post-CLP. Meanwhile, the numbers of CD86+ cells (marker of macrophage activation) in macrophage population were decreased at 5 days post-CLP and increased at 12 days post-CLP. These implied early innate immune exhaustion (day 1-5 post-CLP) with the late immune reconstitution (12 days of CLP). Hence, fungi were introduce at 5 days post-CLP. Indeed, higher susceptibility to C. albicans and A. fumigatus at 5 days post-CLP was demonstrated by survival study and organ injuries, respectively, suggesting an impact of secondary fungal infection post-sepsis. Amphotericin B treatment alone was not effective to treat the CLP-mice with secondary aspergillosis. In contrast, the adjunctive treatment with anti-PD-1 attenuated the disease severity. PD-1 blockade attenuated immune exhaustion in spleens as determined by increased CD86 expression, augmented serum IFN-γ and dampened serum IL-10. In addition, anti-CD3 restimulated splenocytes from anti-PD-1 treated mice highly produced IFN-γ and reduced IL-10 production.

Conclusion: Our study provide fundamental knowledge about macrophage exhaustion and reactivation as a significant determinant for susceptibility to secondary fungal infection. The adjunctive anti-PD-1 treatment in mice with secondary fungal infection presumably reinvigorated exhausted antigen-presenting cells and T cells by upregulating CD86 expression and IFN-g production, diminished IL-10 production, and attenuated disease severity. The adjunctive anti-PD-1 therapy may be expedient for the advanced immunotherapy against lethal fungal infection.