Immunosuppression contributes to the mortality of sepsis. However, the underlying mechanism remains unclear.

In the present study, we investigated the role of inhibitory receptor immunoglobulin-like transcript 5 (ILT5) in sepsis. We first screened the expression of ILT family members, and we found that ILT5 was dramatically up-regulated in the peripheral blood mononuclear cells from sepsis patients versus healthy donors.

Knockdown of ILT5 by small interfering ribonucleic acid increased bacterial killing and reactive oxygen species production in THP-1 and RAW264.7 cells. Moreover, ILT5-expressing monocytes/macrophages exhibited lower expression of antigen-presenting molecules including major histocompatibility complex-II and CD80. In the in vitro coculture system with monocytes/macrophages, blockage of ILT5 facilitated Th1 proliferation and differentiation of CD4⁺ T cells. Furthermore, in vivo experiments demonstrated that pretreatment with ILT5 blocking peptide improved the survival and pulmonary pathology of septic mice.

Together, our study identified ILT5 as an immunosuppressive regulator during sepsis, which may provide potential therapeutic strategy for sepsis.