To the Editor:Regulatory T-cells (Tregs),a subset of CD4+ T-cells,have the capacity to actively suppress immune responses and play a pivotal role in sepsis-induced immunosuppression.[1] B-and T-lymphocyte attenuator (BTLA) is a co-inhibitory receptor that is known to potently inhibit CD4+ T-cell function and to block prosurvival signaling in CD4+ T-cells.[2] Tregs constitutively express BTLA.It has been reported that the absence of BTLA expression on Tregs resulted in reduced interleukin-l 0 production by Tregs in a model of established experimental autoimmune encephalomyelitis.[3] However,the role of BTLA expression on Tregs in patients with sepsis has rarely been investigated.In this study,we investigated the dynamic changes in BTLA expression on Tregs on days 1 and 7 during sepsis and explored the potential role of BTLA expression on Tregs.We used the combination of the surface markers CD4,CD25,and CD127 to identify Tregs.