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

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(d) haplotype was stably transfected into the mouse RAW macrophage cell line, termed RAW-CE16(d) cells. Combining RAW-CE16(d) cells with Ly49 expressing reporter cells demonstrated Ly49i4 and Ly49s4 specificity for CE16(d). The Ly49s4/i4:CE16(d) 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(d) after infection. LM infection and IFN-γ stimulation both led to enhanced CE16(d) expression on the surface of transfected RAW-CE16(d) cells. Interestingly, the reporter cells displayed increased response to LM-infected RAW-CE16(d) cells compared with IFN-γ-treated RAW-CE16(d) cells, suggesting a fundamental difference between these stimuli in supporting enhanced Ly49 recognition of CE16(d). Collectively, our data show that Ly49s4 and Ly49i4 recognize the non-classical RT1-CE16(d) molecule, which in turn is up-regulated during LM infection and thereby may contribute to NK-mediated responses against infected cells.