The role of TIM3+ NK and TIM3- NK cells in the immune pathogenesis of severe aplastic anemia.

Background: Natural killer (NK) cells play important immunoregulatory roles in the immune pathogenesis of severe aplastic anemia (SAA). Our previous research showed that SAA caused a decrease in T cell immunoglobulin mucin-3 (TIM3) expression on NK cells. Here we investigated the expression of surface receptors, and the cytotoxicity of peripheral TIM3⁺ NK and TIM3^- NK cells in patients with SAA.

Methods: The expressions of surface receptors and cytoplasmic protein of TIM3⁺ NK and TIM3^- NK cells from peripheral blood were detected by FCM. The functions of mDCs, and apoptosis rate of K562 cells after co-culture with TIM3⁺ NK and TIM3^- NK cells were maesured by FCM. Westren-blot was used to detect the changes of TIM3⁺ NK and TIM3^- NK signaling pathway proteins (AKT, P-AKT) and compare the functional activity of the two groups.

Results: Activating receptors NKG2D and Granzyme B were higher, while inhibiting receptors NKG2A, CD158a and CD158b were lower on TIM3^- NK cells compared with TIM3⁺ NK cells in patients with SAA. In SAA, the expression of CD80 and CD86 on mDCs (Myeloid dendritic cells) was significantly decreased after incubation with TIM3^- NK cells. The apoptosis rate (AR) of K562 cells was significantly increased after being incubated with TIM3^- NK cells in SAA. The level of signal pathway protein AKT of TIM3^- NK cells in SAA was similar to that of TIM3⁺ NK cells, and the levels of P-AKT and P-AKT/AKT ratio of TIM3^- NK cells were significantly higher than those of TIM3⁺ NK cells.

Conclusions: Therefore, TIM3 exerts its inhibitory effect on NK cells and participates in the immune pathogenesis of SAA. Low expression of TIM3 contributes to the enhancement of NK cell activity which in turn inhibits the immune activation state of SAA and improves the disease state. Our research may aid the development of new therapeutic strategies based on TIM3-NK cells infusion for the treatment of SAA.