Several activating Ly49 receptors recognize an MCMV-infected cell based on the presence of the m04/gp34 viral peptide within a specific H-2 context. (A) Percentages (mean ± SD) of GFP expression by reporter cells carrying individual Ly49 receptors upon co-culture with MEF cells of the H-2^f (top), H-2^k (middle), or H-2^d (bottom) haplotype under the following conditions: uninfected (∅), IFN-γ pretreated (200 U), or infected at an MOI of 0.5 with WT, Δm04, or Δm04Δm06Δm152 MCMV. (B) GFP expression by reporter cells carrying individual Ly49 receptors upon co-culture with H-2^k MEF cells that are either uninfected (thin line) or WT MCMV infected (gray filled line) in the absence (top) or presence of H-2D^k or H-2K^k blocking antibody (middle) or isotype control (bottom). (C) Sequence alignment of the predicted H-2-binding region of Ly49 NKDs based on the Ly49A:H-2D^d crystal structure. Conserved residues between the Ly49 receptors are shown as dashes. Secondary structure elements are denoted by loops (white rectangles) and β-strands (gray ovals). Downward arrows represent putative MHC class I contact sites, whereas boxed residues delimit the NXT N-glycosylation motif. Residues in red represent amino acids unique in Ly49 receptors recognizing the infection in an m04/gp34–H-2–dependent manner. Sequences were retrieved from GenBank with the following accession nos.: Ly49D^B6, AF349733.1; Ly49D^NOD, AF218078.1; Ly49D1^PWK, AY860975.1; Ly49L2^BALB, AF204266; Ly49M^NOD, AF283252.1; Ly49P^MA/My, AY971807.1; Ly49P1^NOD, AF218080.1; Ly49R^MA/My, AF288377.1; and Ly49W^NOD, AF283250.1. Results from one of at least three experiments are shown.