B and T lymphocyte attenuator expression was induced on CD4+T cells and B cells 72 hours following cecal ligation and puncture and was associated with the loss of these cells. Splenic CD4+ T-cell (A) and B-cell (D) B and T lymphocyte attenuator (BTLA) expression was evaluated 72 hours post surgery. As expected, BTLA was induced on CD4+ T cells (A) and B cells (D) (mean fluorescent intensity values presented in Table 2). Concomitantly, a significant decrease in the CD4+ T-cell (B) and B-cell (E) numbers at 72 hours following cecal ligation and puncture (CLP) (n = 10) was observed when compared with sham mice (n = 6). Additionally, significantly lower peripheral blood CD4+ T-cell (C) and B-cell (F) numbers were also observed at this time point. Data are mean ± standard error of the mean. *P <0.05 using an unpaired, two-tailed Student’s t test. Representative flow histograms: filled grey, isotype control; dashed line, sham mouse; black line, CLP mouse.