Heterogeneity of Effector Phenotype for Acute Phase and Memory Influenza A Virus-Specific CTL

Abstract

Ag-specific, CD8+ CTLs clear influenza A viruses from the lung via granzyme (Gzm) and perforin-dependent mechanisms. Ex vivo analysis of perforin-Gzm mRNA profiles demonstrated substantial heterogeneity in patterns of effector mRNA transcription of CD8+ DbNP366- or DbPA224-specific CTL. The only difference between the two epitope-specific sets was apparent very early after infection with similar molecular profiles seen in peak primary and secondary responses and in long-term memory. Surprisingly, memory T cells also expressed a diverse pattern of effector mRNA profile with an emphasis on GzmB and, surprisingly, GzmK. This analysis thus defines how naive, effector, and memory T cells differ in cytotoxic potential and provides novel insight into the molecular signatures of effector molecules observed at various stages after infection.

Granzyme A expression reveals distinct cytolytic CTL subsets following influenza A virus infection

“…These data support the notion that the different grz family members are regulated independently. Previous analysis of effector mRNA expression has demonstrated that there is heterogeneity of grz/pfp expression within virus-specific CTL, with little evidence of effector mRNA co-expression [7,8,12,25]. To date, this heterogeneity has not been examined at the protein level for murine virus-specific CTL.…”

“…Of interest would be to extend this type of analysis to other grz. For example, grzK is implicated in anti-viral CTL immunity based on transcriptional data [7,8,12,34]. Investigation of cytolytic protein expression by CTL will enable in-depth understanding of these proteins that are critical for viral clearance.…”

“…Although previous reports have demonstrated that influenza-specific memory CTL express little grzB protein [8], this has not been determined for grzA. The expression of grzA and/or grzB by splenic or lung-resident influenza A virusspecific memory CTL was assessed.…”

“…Single virus-specific CTL display distinct and heterogeneous patterns of pfp and grz mRNA transcripts after in vitro and in vivo activation [8,12,17,18]. Heterogenous patterns of effector mRNA expression are thought to reflect independent regulatory mechanisms.…”

“…Naïve CTL express grzB early after antigen encounter [3,4], with both increased mRNA and protein expression correlating with progressive cell division [5][6][7]. Although effector CTL express abundant levels of grzB protein at the peak of the response [8], this is largely turned off as the CTL population contracts into memory [9][10][11][12]. Given its important role in CTL-mediated killing, many viruses have evolved strategies that target and disable grzB function [13].…”