Multiple Inhibitory Pathways Contribute to Lung CD8+ T Cell Impairment and Protect against Immunopathology during Acute Viral Respiratory Infection

Abstract

Viruses are frequent causes of lower respiratory infection (LRI). Programmed cell death-1 (PD-1) signaling contributes to pulmonary CD8+ T cell (TCD8) functional impairment during acute viral LRI, but the role of TCD8 impairment in viral clearance and immunopathology is unclear. We now find that human metapneumovirus (HMPV) infection induces virus-specific lung TCD8 that fail to produce effector cytokines or degranulate late after infection, with minimally increased function even in the absence of PD-1 signaling. Impaired lung TCD8 upregulated multiple inhibitory receptors, including PD-1, LAG-3, TIM-3, and 2B4. Moreover, co-expression of these receptors continued to increase even after viral clearance, with most virus-specific lung TCD8 expressing ≥3 inhibitory receptors on day 14 post-infection. Viral infection also increased expression of inhibitory ligands by both airway epithelial cells and antigen presenting cells, further establishing an inhibitory environment. In vitro antibody blockade revealed that multiple inhibitory receptors contribute to TCD8 impairment induced by either HMPV or influenza virus infection. In vivo blockade of TIM-3 signaling failed to enhance TCD8 function or reduce viral titers. However, blockade of LAG-3 in PD-1-deficient mice restored TCD8 effector functions but increased lung pathology, indicating that LAG-3 mediates lung TCD8 impairment in vivo and contributes to protection from immunopathology during viral clearance. These results demonstrate that an orchestrated network of pathways modifies lung TCD8 functionality during viral LRI, with PD-1 and LAG-3 serving prominent roles. Lung TCD8 impairment may prevent immunopathology but also contribute to recurrent lung infections.

Persistence in Temporary Lung Niches: A Survival Strategy of Lung-Resident Memory CD8+T Cells

“…Thus, the level of residual antigen presentation must be lower than that exhibited during a typical chronic infection. In line with this, PD-1 as well as other potential inhibitory molecules may act to prevent excessive immunopathology (26,27,29) by maintaining the cells in a quiescent state (49). Furthermore, reactivation of CD8 + T RM cells in the lung leads to sustained expression of interferon-induced transmembrane protein (IFITM3), which is involved in conferring resistance against subsequent virus infection (132).…”

The CD8 T Cell Response to Respiratory Virus Infections

“…Together, these studies demonstrate a critical role for PD-1 in the suppression of CD8 T cell-mediated immunopathology and cytokine production in both mice and humans. In the absence of PD-1 signaling following HMPV infection, CD8 T cell IFN-γ production remains impaired, suggesting the involvement of compensatory inhibitory pathways ( 140 ). Antigen-specific lung CD8 T cells express inhibitory receptors Tim-3, LAG-3, and 2B4 following HMPV infection and exhibit enhanced cytokine production following in vitro blockade of each receptor individually ( 140 ).…”

“…In the absence of PD-1 signaling following HMPV infection, CD8 T cell IFN-γ production remains impaired, suggesting the involvement of compensatory inhibitory pathways ( 140 ). Antigen-specific lung CD8 T cells express inhibitory receptors Tim-3, LAG-3, and 2B4 following HMPV infection and exhibit enhanced cytokine production following in vitro blockade of each receptor individually ( 140 ). In vivo blockade of LAG-3 partially restored CD8 T cell IFN-γ production in PD-1-deficient mice following HMPV infection ( 140 ).…”

“…Antigen-specific lung CD8 T cells express inhibitory receptors Tim-3, LAG-3, and 2B4 following HMPV infection and exhibit enhanced cytokine production following in vitro blockade of each receptor individually ( 140 ). In vivo blockade of LAG-3 partially restored CD8 T cell IFN-γ production in PD-1-deficient mice following HMPV infection ( 140 ). Tim-3 has also been demonstrated to be critical in suppressing CD8 T cell responses in vivo , as Tim-3 receptor (Galectin-9)-deficient mice exhibited significantly enhanced CD8 T cell responses following both primary and secondary IAV infections ( 141 ).…”

Suppression of Cytotoxic T Cell Functions and Decreased Levels of Tissue Resident Memory T cell During H5N1 infection

“…PD-1 interactions with PD-L1 have been demonstrated to suppress cytotoxic CD8+ T cell functions (42-44). PD-L1 expression is induced during viral infection on a variety of cell types including monocytes, DC, macrophages and epithelial cells(43-46). In our analysis of cell types expressing PD-L1, we observed higher PD-L1 expression on Ly6C hi inflammatory monocytes isolated from H5N1 (2:6) infected mice as compared to H1N1 infected mice (Figure 4C).…”