The authors used a model of Toxoplasma gondii infection in which mice that contained fluorescently labelled naive T cells specific for ovalbumin (OVA) were first challenged with irradiated parasites and then infected with live fluorescent parasites, both of which expressed OVA. This allowed the authors to visualize the behaviour of memory T cells during a recall response.
As previously described, the parasites were found in subcapsular sinus (SCS) macrophages in the draining lymph node 5 hours after infection. Analysis of T cell localization in the draining lymph node during the recall response showed that memory T cells migrated more rapidly and accumulated more extensively than naive T cells at the SCS; this migration was shown to be antigen independent. In addition, as early as 5 hours after infection, both naive and memory T cells formed stable clusters with parasite-containing cells (mainly dendritic cells and macrophages) in an antigen-dependent manner. Furthermore, the authors observed direct parasite invasion of both naive and memory T cells that were in contact with infected target cells. More memory T cells than naive T cells were infected with T. gondii, and antigen recognition enhanced T cell invasion by the parasites. T cells that contained parasites remained motile and approximately half of the infected leukocytes in the draining lymph nodes and blood 5–7 days after oral infection were T cells.
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