letter. 42 nature genetics ⢠volume 28 ⢠may 2001. Susceptibility to mouse cytomegalovirus is associated with deletion of an activating natural killer cell receptor.
© 2001 Nature Publishing Group http://genetics.nature.com
letter
Seung-Hwan Lee1, Sonia Girard1, Denis Macina1, Maria Busà1, Ahmed Zafer1, Abdelmajid Belouchi2, Philippe Gros3 & Silvia M. Vidal1
Cytomegalovirus is the leading cause of congenital viral disease and the most important opportunistic infection in immunocompromised patients1,2. We have used a mouse experimental infection model (MCMV) to study the genetic parameters of host/virus interaction. Susceptibility to infection with MCMV is controlled by Cmv1, a chromosome 6 locus that regulates natural killer (NK) cell activity against virally infected targets3–5. Here, we use a positional cloning strategy to isolate the gene mutated at the Cmv1 locus. Cmv1 maps within a 0.35-cM interval defined by markers D6Ott8 and D6Ott115, which corresponds to a physical distance of 1.6 Mb (refs. 6–8). A transcript map of the region identified 19 genes8, including members of the killer cell lectin-like receptor family a (Klra, formerly Ly49; refs. 9–12), which encode inhibitory or activating NK cell receptors that interact with MHC class I molecules13–15. Klra genes have different copy numbers and genomic organization, and are highly polymorphic among inbred strains, making it difficult to distinguish between normal allelic variants and distinct Klra genes15–17, or possible mutations associated with Cmv1. The recombinant inbred strain BXD-8/Ty (BXD-8; ref. 18), derived from Cmv1r C57BL/6 (B6, resistant) and Cmv1s DBA/2 (susceptible), is of particular interest because it is highly susceptible to MCMV infection despite having a B6 haplotype at Cmv1. We determined that MCMV susceptibility in BXD-8 is associated with the deletion of Klra8 (formerly Ly49h).
a
We investigated the mode of inheritance of the BXD-8 susceptibility trait in F1 and F2 progeny issued from crosses to MCMV-resistant B6 and MCMV-susceptible DBA/2 progenitors. As measured by spleen viral loads (Fig. 1a), all (BXD-8×B6)F1 mice were resistant, whereas all (BXD-8×DBA/2)F1 were susceptible. Among the (BXD8×B6) F2 population, 40 of 117 animals (34%) were susceptible, independent of gender (Fig. 1b), showing that MCMV susceptibility in BXD-8 is controlled by a single, autosomal recessive locus. A genome-scan approach in (BXD-8×B6)F2 mice localized a single locus in the vicinity of D6Mit290 (lod score=29.1) accounting for 68% of the phenotypic variance. All but 5 (Fig. 1c) F2 mice with spleen plaque-forming units (PFU) counts greater than 104 were homozygous for the BXD-8 allele, whereas those with viral titers less than 104 were either heterozygous or B6 homozygous at D6Mit290. Because D6Mit290 maps 0.6 cM distal from Cmv1 (refs. 5,6), these results indicate that either Cmv1 or a closely linked gene is responsible for susceptibility to MCMV infection in BXD-8. To better localize the BXD-8 susceptibility locus, F1 progeny of BXD-8 and two congenic C.B6-Cmv1r strains were tested for susceptibility to MCMV (Fig. 2a). Whereas (BXD-8×BALB/c)F1 showed high spleen viral titers (105), hybrids of BXD-8 F1 and either of the two C.B6-Cmv1r congenics were resistant to infection (PFU counts
