Alloreactive donor T cells infiltrate the testis during an acute GVHR. Acute GVHD was induced as in Figure 1. (A,B) Frozen sections from testicular tissues were analyzed at 2 weeks after transplantation for the presence of CD3ϵ⁺ cells in mice without (A) and with (B) GVHD. A cluster of CD3⁺ T cells present in the interstitial space between the seminiferous tubules is highlighted in panel B. Original magnification × 100 (magnification for inset × 300). (C) Donor T cells are present in testis. Colocalization of CD3ϵ and CD45.1 was detected by confocal microcopy in mice that received allogeneic transplants. The panel shows cells that stain simultaneously for red (CD3/Cy3) and green (CD45.1/FITC) color. Original magnification × 630. (D) Analysis of cytokine mRNA expression by quantitative PCR. Transcripts for IFN-γ and TNF-α were measured in frozen testicular tissue isolated from mice at 2 to 4 weeks after T-cell infusion. The y-axis represents the x-fold increase of cytokine mRNA in mice with acute GVHD when compared with mice without GVHD (normal transcriptional activity is set as 1). Mean ± SD. (E,F) Frozen sections from testicular tissues were analyzed at 2 weeks after transplantation for the presence of CD11b⁺ cells (shown in red) in mice without (E) and with (F) GVHD. Original magnification × 200. B6D2F₁ mice infused with syngeneic (□) or allogeneic (▪) donor T cells.