SHIP Influences Signals from CD48 and MHC Class I Ligands That Regulate NK Cell Homeostasis, Effector Function, and Repertoire Formation

Abstract

Previously, we showed that 2B4 is a dominant inhibitory receptor in SHIP-deficient NK cells that prevents efficient cytolysis of complex targets. We show in this study that 2B4 deficiency restores homeostatic control and cytolytic function to SHIP-deficient NK cells. However, 2B4−/−SHIP−/− NK cells still exhibit a profound disruption of their NK receptor repertoire and are compromised for induction of IFN-γ by several NK-activating receptors, including NKp46, NK.1.1, and NKG2D. In addition, we find that 2B4−/− NK cells have an extensively disrupted repertoire, including a supernormal frequency of NKp46+ NK cells. Consequently IFN-γ is induced on a much higher percentage of 2B4−/− NK cells following engagement of NKp46. We also find that both SHIP and 2B4 are required to prevent expression of Ly49B, a myeloid lineage MHC class I receptor not normally expressed by the NK lineage. Finally, when SHIP-deficient NK cells are on an H-2d background, they exhibit supernormal levels of Ly49A and possess normal cytolytic function against MHC-matched tumor targets and enhanced cytolysis of MHC mismatched tumor targets. However, despite normal or elevated cytolytic function, H2d SHIP−/− NK cells exhibit poor induction of IFN-γ like their H2b+ or 2B4−/− counterparts, demonstrating a uniform requirement for SHIP in induction of IFN-γ downstream of key NK activating receptors. These findings reveal a complex interplay of SHIP, 2B4, and MHC in the regulation of homeostasis, effector function, and repertoire formation in the NK cell lineage.

Mouse natural killer cell development and maturation are differentially regulated by SHIP-1

“…KLRG1, a marker for the most mature NK cells, was also weakly expressed on SHIP-1 Ϫ/Ϫ NK cells (supplemental Figure 3B-C) and observed previously in germ line SHIP-1 Ϫ/Ϫ mice on a C57BL6 background. 24 Collectively, these data suggest that SHIP-1 regulates NK cell transition from immature to mature NK cells. NK precursors were also reduced in SHIP-1 Ϫ/Ϫ mice ( Figure 2).…”

“…For instance, 2B4/CD48 interaction has been shown to influence NK cell homeostasis. 24 Regardless of the mechanism, our data reveal both an indirect role and direct role for SHIP-1 at different checkpoints of NK cell development.…”

“…For instance, 2B4/CD48 interaction has been shown to influence NK cell homeostasis. 24 Regardless of the mechanism, our data reveal both an indirect role and direct role for SHIP-1 at different checkpoints of NK cell development.Our results also reveal that the decreased functionality of SHIP-1 Ϫ/Ϫ NK cells can be rescued in chimeric mice except when stimulated with IL-12 and IL-18. In this context, our data show that SHIP-1 Ϫ/Ϫ NK cell IFN-␥ production is decreased at all stages of maturation, suggesting it is because of an intrinsic defect and not uniquely to a maturation phenotype.…”

“…[20][21][22][23] In addition, previous studies demonstrate the importance of SHIP-1 in the generation of the NK cell receptor repertoire. 14,24,25 We therefore hypothesized that SHIP-1 may play a role in NK cell development and maturation. To test this hypothesis, we examined lymphocyte populations in the spleen, blood, liver, and bone marrow of SHIP-1 ϩ/ϩ , SHIP-1 ϩ/Ϫ , and SHIP-1 Ϫ/Ϫ mice.…”

“…No difference in bone marrow expression of CD94 and Ly49s, as well as splenic expression of CD94 was observed, but there was a significant decrease in splenic expression of Ly49s in SHIP-1 Ϫ/Ϫ mice compared with controls (Table 1 and supplemental Figure 2C-E) as reported previously. 24 We also looked at H2-K b and H2-D b expression in total splenocytes as well as splenic NK cells (supplemental Figure 2F). SHIP-1 Ϫ/Ϫ total splenocytes and splenic NK cells (as well as B, T, and dendritic cells; data not shown) express equivalent levels of MHC class I molecules as controls.…”