Previously called Mhv-1, Hv2. This locus controls resistance of neurons and macrophages to infection by the JHM and A59 strains of mouse hepatitis virus MHV-4. The allele Ceacam1^Hv2-r determines resistance and has been found only in the SJL/J strain; the strains A/J, C57BL/10, BALB/c, NZB, DBA/2, AKR/J, CBA/J, C3H/He, and SWR are all susceptible to infection (Ceacam1^Hv2-s. Heterozygotes are fully susceptible (J:6451, J:14870, J:7456).