The Activated Type 1–Polarized Cd8⁺ T Cell Population Isolated from an Effector Site Contains Cells with Flexible Cytokine Profiles

The capacity of activated T cells to alter their cytokine expression profiles after migration into an effector site has not previously been defined. We addressed this issue by paired daughter analysis of a type 1–polarized CD8⁺ effector T cell population freshly isolated from lung parenchyma of influenza virus–infected mice. Single T cells were activated to divide in vitro; individual daughter cells were then micromanipulated into secondary cultures with and without added IL-4 to assess their potential to express type 2 cytokine genes. The resultant subclones were analyzed for type 1 and 2 cytokine mRNAs at day 6–7. When the most activated (CD44^highCD11a^high) CD8⁺ subpopulation from infected lung was compared with naive or resting (CD44^lowCD11a^low) CD8⁺ cells from infected lung and from normal lymph nodes (LNs), both clonogenicity and plasticity of the cytokine response were highest in the LN population and lowest in the activated lung population, correlating inversely with effector function. Multipotential cells were nevertheless detected among clonogenic CD44^highCD11a^high lung cells at 30–50% of the frequency in normal LNs. The data indicate that activated CD8⁺ T cells can retain the ability to proliferate and express new cytokine genes in response to local stimuli after recruitment to an effector site.