Impaired CD4⁺ T-cell expansion leads to prolonged graft survival.

<p>Impaired proliferation of alloantigen-specific CD4⁺ T-cells leads to prolonged graft survival in old skin graft recipients. Nude B6 mice were engrafted with two bm12 skin transplants following adoptive transfer of young or old 2×10⁶ transgenic CD4⁺ ABM T-cells. In line with the reduced CD4⁺ T-cell response in old WT recipients skin graft survival was significantly prolonged following transfer of old alloreactive CD4⁺ T-cells (<b>A</b>). One week after transplantation spleen, dLN and ndLN were harvested and leukocytes were stained for CD4⁺, Vα2⁺ and Vβ8⁺ expression to assess proliferation of adoptively transferred T-cells (<b>B</b>). In parallel, skin grafts were stained for graft infiltrating CD4⁺ T-cells (<b>C</b>). At day 7, absolute numbers of adoptively transferred CD4⁺ T-cells were counted in different lymphatic compartments in order to determine T-cell proliferation. A significantly reduced proliferation of old tg CD4⁺ T-cells was accompanied by decreased graft infiltration, underscoring a delayed rejection response (<b>B</b> and <b>C</b>).