Abstract
Purpose: :
Herpes simplex virus type 1 (HSV-1) latent infection of sensory neurons provides the source of virus for recurrent herpetic eye disease. The generation and maintenance of a HSV-specific memory CD8+ T cell population is critical for immunosurveillance of HSV-1 latently infected neurons in the trigeminal ganglion (TG). Understanding the role of CD4+ T cells in programming or maintaining CD8+ T cell memory will have important implications for vaccine development.
Methods: :
C57BL/6 mice were depleted of CD4+ T cells in vivo starting before or 8 days after HSV-1 corneal infection (8 dpi). The size and functionality of the HSV-specific CD8+ T cell effector and memory populations were tested by gB498-505 tetramer staining and intracellular cytokine staining and flow cytometric analysis following in vitro stimulation
Results: :
the lack of early (prior to 8 dpi) CD4+ T cell "programming" gave rise to HSV-specific CD8+ T cell effector (8 dpi) and early memory (≤ 34 dpi) populations in TG that were quantitatively normal, but exhibited functional compromise (responded only to a high epitope density despite normal TCR affinity) mediated by PD-1/PD-L1 interaction. The CD8+ T cell functional compromise was transient (recovered by 56 dpi) and associated with failure to maintain viral latency. Late CD4+ T cell depletion (beginning 8 dpi) had no effect on CD8+ T cell memory or viral latency.
Conclusions: :
CD4+ T cells are needed for programming, but not for the maintenance of HSV-specific CD8+ T cell memory. PD-1 expression inhibits the capacity of unhelped CD8+ T cells to respond to low epitope densities likely present on latently infected neurons, and compromises their ability to maintain HSV-1 latency.
Keywords: immunomodulation/immunoregulation • herpes simplex virus • microbial pathogenesis: experimental studies