Mouse Hepatitis Virus Receptor as a Determinant of the Mouse Susceptibility to MHV Infection

Taguchi, Fumihiro; Hirai-Yuki, Asuka

The above data suggested to us that CEACAM1 is an important factor to determine the susceptibility of mice and could be a product of the gene responsible for susceptibility mapped in a locus on chromosome 7 by Smith et al. (1984) . This idea is strengthened by the fact that the MHV receptor Ceacam1 gene is mapped to the same region on chromosome 7 (Robbins et al., 1991) . If the CEACAM1 receptor is a determinant of susceptibility, and susceptibility is dominant over resistance, then mice with CEACAM1a/CEACAM1a and CEACAM1a/CEACAM1b are susceptible and only mice with a CEACAM1b/CEACAM1b phenotype, such as SJL mice, are resistant. To assess this possibility, we have mated BALB/c and SJL to generate F1 mice, and then we obtained mice backcrossed to SJL. We also produced F2 mice from BALB/c and SJL mice. By using these mice, we examined the relationship between the mouse genotype of Ceacam1 and its susceptibility to MHV. Of more than 120 backcrossed and F2 mice, those with Ceacam1a/Ceacam1a and Ceacam1a/Ceacam1b were fully susceptible, while those with Ceacam1b/Ceacam1b were resistant (Ohtsuka and Taguchi, 1997) . These experimental results are well in accordance with the hypothesis, i.e., that mouse susceptibility to MHV is determined by a receptor gene. We have also Frontiers in Microbiology | Virology studied the relationship between MHV susceptibility and CEA-CAM1 allelic forms by using wild mice (Ohtsuka et al., 2001) . The study showed that most of subspecies of wild mice distributed worldwide express both or either CEACAM1a and CEACAM1b. Among those mice, CEACAM1a-expressing ones showed high susceptibility to MHV, while those with CEACAM1b were not highly susceptible, being in good agreement to the result and hypothesis obtained by mouse cross and backcross experiment shown above.