Major histocompatibility complex class I-restricted protection against murine cytomegalovirus requires missing-self recognition by the natural killer cell inhibitory Ly49 receptors

Abstract

16Viruses have evolved strategies that highlight critical, intertwined host immune mechanisms. As 17 postulated by the missing-self hypothesis, natural killer (NK) cells and major histocompatibility complex 18 class I (MHC-I)-restricted cytotoxic T lymphocytes (CTLs) have opposing requirements for ubiquitously 19 expressed MHC-I molecules. Since NK cell MHC-I-specific Ly49 inhibitory receptors prevent killing of cells 20 with normal MHC-I, viruses evading CTLs by down-regulating MHC-I should be vulnerable to NK cells. 21However, definitive integrated in vivo evidence for this interplay has been lacking, in part due to 22 receptor polymorphism and a proposed second function of Ly49 receptors in licensing NK cells via self-23 MHC-I. Here we generated mice lacking specific Ly49 inhibitory receptors to show their essential role in 24 licensing and controlling murine cytomegalovirus (MCMV) infection in vivo in an MHC-restricted 25 manner. When MCMV cannot down-regulate MHC-I, NK cells cannot control infection that instead is 26 mediated by CTLs, as predicted by the missing-self hypothesis.control of Δm157-MCMV requires cytotoxicity, implying direct target contact, but NKG2D was not 96 required. 97 98 NK cell resistance requires Ly49 receptor expression 99Since Ly49s recognize MHC-I, we assessed their candidacy for being responsible for the MHC-I-100 restricted, NK-dependent resistance to Δm157-MCMV by using CRISPR-Cas9 to target their deletion 101 directly in B6 zygotes. When we used a guide RNA (gRNA) intentionally chosen for its promiscuity for 102 several Ly49s, we generated ΔLy49-1 mice with two distinct deletions: 1) 149kb deletion between Ly49a 103and Ly49g with an out-of-frame fusion; and 2) 66Kb deletion between two pseudogenes, Ly49n (Klra14-104 ps) and Ly49k (Klra11-ps), such that Ly49h was deleted (Fig 2A). Flow cytometry confirmed the loss of 105Ly49A, Ly49C, Ly49G, and Ly49H expression. Ly49D expression was markedly decreased but its coding 106 sequence was intact, suggesting an as yet unidentified locus control region within one of the deleted 107 segments. We also generated single and compound Ly49 deleted mice, detailed below (Fig S1 and Fig 108 S2). Predicted potential off-target sites were absent by PCR amplification and sequencing (Table S1). To 109 further eliminate any off-target effects and genetic mosaicism, we backcrossed all CRISPR-Cas9 founder 110 mice to WT B6 for two generations followed by additional crosses to KODO mice, then D8 (H2D d ) 111 transgenic mice, to generate the indicated homozygous Ly49 knockout mice on the D8-KODO 112 background. 113 114 MHC-restricted, NK cell-dependent resistance to Δm157-MCMV in D8-KODO mice was absent in ΔLy49-1 115 D8-KODO mice (Fig 2B). Additionally, KODO mice with intact Ly49s complemented ΔLy49-1 D8-KODO 116 mice as their F1 hybrids showed fully restored Δm157-MCMV resistance (Fig 2B), indicating that 117 heterozygous expression of Ly49A, Ly49C, Ly49G, Ly49H (Fig S2), deleted in ΔLy49-1, was sufficient for

Tissue-Resident NK Cells: Development, Maturation, and Clinical Relevance

“…The distribution of these subsets among the cNK and trNK differs significantly. Inhibitory receptors such as human killer immunoglobulin-like inhibitory receptors (KIR) [ 60 ] and murine Ly49s [ 61 ] primarily recognize classical Major Histocompatibility Complex Class I (MHC-I) and form the basis for ‘licensing’ that allows NK cells to differentiate between ‘self’ and ‘non-self’ [ 5 , 6 , 7 , 8 , 9 ]. Notably, cNK and trNK cells express differing levels or types of KIRs, emphasizing the potential divergent effector functions of these subsets.…”