Listeria monocytogenes infection enhances the interaction between rat non-classical MHC-Ib molecule and Ly49 receptors

Abstract

Murine NK cell Ly49 receptors, functionally analogous to KIRs in humans recognize MHC class I molecules and play a key role in controlling NK cell function. We have previously shown that the paired activating Ly49s4 and inhibitory Ly49i4 receptors recognize undefined non-classical MHC-Ib ligands from the RT1-CE region in rats. Here, the RT1-CE16 gene of the RT1 haplotype was stably transfected into the mouse RAW macrophage cell line, termed RAW-CE16 cells. Combining RAW-CE16 cells with Ly49 expressing reporter cells demonstrated Ly49i4 and Ly49s4 specificity for CE16. The Ly49s4/i4:CE16 interaction was confirmed by specific MHC-I blocking monoclonal Abs. Further, we used our in vitro model to study the effect of Listeria monocytogenes (LM) on CE16 after infection. LM infection and IFN-γ stimulation both led to enhanced CE16 expression on the surface of transfected RAW-CE16 cells. Interestingly, the reporter cells displayed increased response to LM-infected RAW-CE16 cells compared with IFN-γ-treated RAW-CE16 cells, suggesting a fundamental difference between these stimuli in supporting enhanced Ly49 recognition of CE16. Collectively, our data show that Ly49s4 and Ly49i4 recognize the non-classical RT1-CE16 molecule, which in turn is up-regulated during LM infection and thereby may contribute to NK-mediated responses against infected cells.

Recognition of Listeria monocytogenes infection by natural killer cells: Towards a complete picture by experimental studies in rats

“…We have reported that LM-infected R2 and CC531 cells, similar to IFN-γ treatment of uninfected cells, displayed increased expression of classical and nonclassical MHC-I molecules, as determined by FACS staining with specific mAbs [43][44][45]73 (summarized in table 1). The enhancement starts after 24 h post infection and reach its maximum level at 72 h that, to our knowledge, was the first clear description of this phenomenon.…”

“… 44 ly49i4 and Ly49s4 receptors are the second pair of activating and inhibitory Ly49 receptors that recognize same ligands encoded in RT1-CE region. 42 , 43 Further alloresponder studies have revealed several new ligands from RT1-CE region for stimulatory and inhibitory Ly49 receptors that are listed in table 1 . 41 One human Ly49 pseudogene has been described.…”

“…In vitro experiments with reporter cell lines, expressing Ly49s5, Ly49s4 or Ly49i4 receptors strongly indicated that increased expression of RT1-CE molecules on infected cells may be detected by Ly49 receptors. 43 –45 However, since each NK cell expresses several stimulatory and inhibitory NK cell receptors, the overall result of NK cell recognition of a target cell will depend on several NK-receptor MHC-I interactions. 78 An indication to support this assumption comes from comparison of IFN-γ production of NK cells against LM -infected RmW and R2-MØ cells.…”

“…After successful RT1-CE16 d surface upregulated expression on LM -infected we observed stronger response by Ly49 receptor compared to IFN-γ upregulated cells which deserve a follow-up-analysis. 43 Theoretically speaking, listerial peptide loaded MHC-I molecules may influence the interaction by conformational changes in MHC-I molecules in which Ly49 recognition enhances. Although NK alloreactivity in mice is regulated primarily by inhibitory Ly49 receptors, activating Ly49 receptors are equally important in rats.…”