Exhausted CD8 T cells downregulate the IL-18 receptor and become unresponsive to inflammatory cytokines and bacterial co-infections

PLoS Pathog. 2011 Sep;7(9):e1002273. doi: 10.1371/journal.ppat.1002273. Epub 2011 Sep 29.

Abstract

During many chronic infections virus-specific CD8 T cells succumb to exhaustion as they lose their ability to respond to antigenic activation. Combinations of IL-12, IL-18, and IL-21 have been shown to induce the antigen-independent production of interferon (IFN)-γ by effector and memory CD8 T cells. In this study we investigated whether exhausted CD8 T cells are sensitive to activation by these cytokines. We show that effector and memory, but not exhausted, CD8 T cells produce IFN-γ and upregulate CD25 following exposure to certain combinations of IL-12, IL-18, and IL-21. The unresponsiveness of exhausted CD8 T cells is associated with downregulation of the IL-18-receptor-α (IL-18Rα). Although IL-18Rα expression is connected with the ability of memory CD8 T cells to self-renew and efflux rhodamine 123, the IL-18Rα(lo) exhausted cells remained capable of secreting this dye. To further evaluate the consequences of IL-18Rα downregulation, we tracked the fate of IL-18Rα-deficient CD8 T cells in chronically infected mixed bone marrow chimeras and discovered that IL-18Rα affects the initial but not later phases of the response. The antigen-independent responsiveness of exhausted CD8 T cells was also investigated following co-infection with Listeria monocytogenes, which induces the expression of IL-12 and IL-18. Although IL-18Rα(hi) memory cells upregulated CD25 and produced IFN-γ, the IL-18Rα(lo) exhausted cells failed to respond. Collectively, these findings indicate that as exhausted T cells adjust to the chronically infected environment, they lose their susceptibility to antigen-independent activation by cytokines, which compromises their ability to detect bacterial co-infections.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • CD8-Positive T-Lymphocytes / immunology*
  • CD8-Positive T-Lymphocytes / metabolism
  • Cytokines / biosynthesis
  • Cytokines / genetics
  • Cytokines / immunology*
  • Down-Regulation / genetics
  • Down-Regulation / immunology*
  • Inflammation Mediators / immunology*
  • Inflammation Mediators / metabolism
  • Interleukin-18 Receptor alpha Subunit / biosynthesis
  • Interleukin-18 Receptor alpha Subunit / genetics
  • Interleukin-18 Receptor alpha Subunit / immunology*
  • Interleukin-2 Receptor alpha Subunit / genetics
  • Interleukin-2 Receptor alpha Subunit / immunology
  • Interleukin-2 Receptor alpha Subunit / metabolism
  • Listeria monocytogenes / immunology*
  • Listeriosis / genetics
  • Listeriosis / immunology*
  • Listeriosis / metabolism
  • Mice
  • Mice, Knockout

Substances

  • Cytokines
  • Il18r1 protein, mouse
  • Il2ra protein, mouse
  • Inflammation Mediators
  • Interleukin-18 Receptor alpha Subunit
  • Interleukin-2 Receptor alpha Subunit