“…The presence of CTLA-4 on CD4 + CD25 + Foxp3 + T cells has been regarded as an explanation for immunosuppression during disease progression in infections with HIV, SIV, HCV, and Trypanosoma and in B cell non-Hodgkin lymphoma (Boasso et al, 2007;Graefe et al, 2004;Kaufmann and Walker, 2009;Leng et al, 2002;Nakamoto et al, 2009;Yang et al, 2006;Zaunders et al, 2006;Zhang et al, 2010). In the model of HTLV-I-related BLV, Foxp3-and CTLA-4-expressing HTLV-I-infected cells suppressed the proliferation of naïve T cells that were stimulated with anti-CD3 antibody (Takayanagi et al, 2009). In the present study, bovine CTLA-4 mRNA was predominantly expressed in CD4 + T cells among cell populations from BLV-infected cattle (data not shown), and the expression of CTLA-4 in CD4 + cells was positively correlated with Foxp3, the most reliable marker for Treg, suggesting that CTLA-4 was expressed by Tregs.…”