Description:
<jats:title>Abstract</jats:title><jats:p>Follicular helper T cells (T<jats:sub>FH</jats:sub>) mediate B cell selection and clonal expansion in germinal centers (GCs), and follicular regulatory T cells (T<jats:sub>FR</jats:sub>) prevent the emergence of self-reactive B cells and help to extinguish the reaction. Here we show that GC reactions continually recruit T cells from both the naïve conventional and naive thymic regulatory T cell (Treg) repertoires. In the early GC, newly recruited T cells develop into T<jats:sub>FH</jats:sub>, whereas cells entering during the contraction phase develop into T<jats:sub>FR</jats:sub> cells that contribute to GC dissolution. The T<jats:sub>FR</jats:sub> fate decision is associated with decreased antigen availability and is modulated by slow antigen delivery or mRNA vaccination. Thus, invasion of ongoing GCs by newly developing T<jats:sub>FH</jats:sub> and T<jats:sub>FR</jats:sub> helps remodel the GC based on antigen availability.</jats:p>