Stenotrophomonas-maltophilia inhibits host cellular immunity by activating PD-1/PD-L1 signaling pathway to induce T-cell exhaustion.

• We first described the S.maltophilia immunosuppressive effect on T cells and it is meaningful for immunosuppressed patients or co-infections. • T cells stimulated by S.maltophilia with CD4 and CD8 degraded via PD-1/PD-L1 pathway, which led to the massive apoptosis of T cells. • T cells were stimulated by S. maltophilia to secrete IFN-γ. Blocking the PD-1/PD-L1 pathway, apoptosis was suppressed. • S.maltophilia down-regulates host immunity by inhibiting immune cells. Smalotrophomonas maltophilia (S. maltophilia) is common in nosocomial infections. However, few studies have revealed the effect of S. maltophilia on cellular immunity in the host's immune system up to now. In clinical work, we accidentally discovered that S. maltophilia directly stimulated T cells to secrete IFN-γ. S. maltophilia was co-cultured with PBMCs to detect secretion of cytokines (IFN-γ, TNF-α and IL-2) and expression of cell surface molecules (CD3, CD4, CD8, CD69, CD147 and CD152) of T cells. We used light microscopy and electron microscopy to observe the cell morphology and subcellular structure of S. maltophilia co-cultured with lymphocytes. Flow cytometry and Western Blot were used to detect the expression of PD-1/PD-L1 and annexin V in cells. T cells stimulated by S. maltophilia secreted a large amount of IL-2, IFN-γ, and TNF-α. The expression of CD4 and CD8 on the cell surface were declined, accompanied by the activation of the PD-1/PD-L1 pathway, which eventually led to the massive apoptosis of T cells. Electron microscopy showed that cells showed significant apoptotic morphology. Blocking the PD-1/PD-L1 pathway can inhibit the apoptosis-inducing effect of S. maltophilia on T cells. These indicates that T cells are inhibited after being stimulated by S. maltophilia , and then accelerated to induce death without the initiation of an immunologic cascade. This paper demonstrates for the first time the inhibitory effect of S. maltophilia on cellular immunity, and the immunosuppressive effect induced by infection of S. maltophilia should be considered. [ABSTRACT FROM AUTHOR]