A genetic analysis was made of the susceptibility of inbred mice to a paralytic disease elicited by the ip injection of a neuroparalytic strain of lactic dehydrogenase virus. The frequency of disease in susceptible inbred mice was X-ray dose and age dependent. Analysis of the susceptibility of appropriate F1 hybrids and their backcross progeny showed that susceptibility was not linked to the major histocompatibility complex but segregated with the Fv-1 linkage group. Linkage group analysis showed that resistance to paralytic infection was linked to a single gene outside the major histocompatibility complex. By determining the segregation of Gpd-1 isozyme variants among backcross progeny it was shown that inheritance of the Fv-1b allele resulted in virtually absolute restriction of susceptibility. Genetic evidence was obtained indicating that mice that mice that had multiple copies of N-tropic C-type retroviruses in their genomes, and that were permissive for retrovirus expression (Fv-1n/n), were susceptible to paralytic LDV infection. Strains that carried few copies of N-tropic C-type retroviruses in their genomes, or that inherited the Fv-1b allele, were resistant. A significant maternal resistance effect was demonstrable in some backcross generations that appeared to be mediated by H-2b in the major histocompatibility complex.
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