Differences in maintenance of CD8+ and CD4+ bacteria-specific effector-memory T cell populations

Abstract

Our knowledge about the kinetics and dynamics of complex pathogen-specific CD8+ T cell responses and the in vivo development of CD8+ memory T cells has increased substantially over the past years; in comparison, relatively little is known about the CD4+ T cell compartment. We monitored and directly compared the phenotypical changes of pathogen (Listeria monocytogenes)-specific CD8+ and CD4+ T cell responses under conditions leading to effective and long-lasting protective immunity. We found that the general kinetics of bacteria-specific CD8+ and CD4+ T cells during the effector and post-effector phases are synchronized. However, later during the memory phase, CD8+ and CD4+ T cell populations differ substantially. Whereas CD8+ memory T cell populations with immediate effector function are readily detectable in lymphoid and non-lymphoid tissues and remain remarkably stable in size, antigen-specific CD4+ effector-memory T cells decline continuously in frequency over time. These findings have important implications for the better understanding of the in vivo development of protective immunity towards intracellular pathogens.