Appearance of rats sensitive to experimental autoimmune encephalomyelitis in a previously resistant strain

Changes are described in the PVG strain with respect to susceptibility for induction of experimental autoimmune encephalomyelitis. During a period of 8 years, the strain changed from a nearly resistant to a partly susceptible strain. Selective breeding of susceptible and resistant rats showed that the cause was genetic. This could also be seen in the susceptibility of F1 hybrids with the resistant Brown-Norway strain; such hybrids were strongly susceptible at the beginning but showed about 40% susceptibility during the later part of the period. It is argued that the genetic changes probably occurred in loci regulating mechanisms of resistance.