BTLA and Sepsis: In contrast to the mouse studies evaluating PD-1 and CTLA-4 in sepsis, we found that BTLA in mice was constitutively expressed on a very high percentage of CD4+ T cells, but the intensity of this expression was further increased in response to CLP, while CD4+ T cells only increased in the percentage of CTLA-4+ and PD-1+ expressing lymphocytes in response to CLP [24,25].