Murine CD4+ T cell clones vary in function in vitro and in influenza infection in vivo.

Several CD4+ Th1 clones specific for influenza haemagglutinin or nucleoprotein were transferred into syngeneic mice after intranasal influenza infection to examine whether they accelerate viral clearance in vivo similarly to CD8+ cytotoxic T cells. We observed changes in functional properties of the CD4+ clones in vitro and variable effects on the course of infection in vivo. While some clones resulted in more rapid virus clearance, others had no protective effect, but rather exacerbated illness symptoms. Our results reflect problems in the in vivo use of CD4+ T cell clones maintained in long-term culture. Their IL-2 and IL-5 release and cytolytic activity varied, while IL-3 and gamma-IFN production as well as DTH induction were more stable. CD4+ T cells primed by infection became cytolytic only after prolonged culture. The data point to the fine balance between exacerbation of disease and protection by CD4+ T cells.