Adaptive immune system is characterized by its ability to recall prior antigen encounter and to mount stronger and swifter response for the second time. This is what typically happens to conventional T cells. But what about regulatory T cells (Tregs)? Do Tregs also display enhanced recall response when encountering [antigen] for the second time?
The answer is NO according to new study from Rudensky's lab published this week in journal Cell. It appears that while phenotypically and gene-expression wise Tregs do resemble conventional memory T cells, nonetheless Tregs do not undergo enhanced recall response when going through the second time encounter.
To test this hypothesis, the authors subjected Tregs to inflammatory environment and tracked their behavior. First, they found that phenotypically Tregs returned to "resting" state within 60 days following activation and resolution of inflammation.
Gene expression analysis confirmed Tregs tested prior to inflammation (resting Tregs) or following inflammation (memory Tregs) resembled each other, while Tregs going through inflammatory process (activated Tregs) had a distinct gene profile.
Functionally too resting Tregs and memory Tregs showed similar potential to inhibit hyper-proliferation of naive T cells when co-transferred into T cell-deficient host.
However, unlike conventional memory CD4 T cells, memory Tregs did not undergo more robust recall response when subjected to inflammation + undefined antigen for the second time.
Finally, the authors observed that Tregs displayed common gene profile with conventional memory CD4 T cells that differentiate them from naive T cells.
In summary, this study suggests two things: first, Tregs do not acquire secondary enhanced recall response capability [at least when exposed to inflammation and undefined antigen] and second, Tregs and conventional memory CD4 T cells share similar gene expression profile.