Originally derived by Dr. Hans J. Hedrich at Versuchstierzucht, Hannover, Germany by transgressing the MHC of DA/Han rats (AV1) into LEW/Han rats for 16 backcross generations. RT1av1 haplotype is a variant to the standard a- haplotype with the difference residing in the atypical MHC class I region.
No macroscopic symptoms were observed in rats injected with IFA emulsified with water but when arthritogenic adjuvants like pristane, mycobacteria, MDP, avridine were added arthritis incidence and severity was increased. Beta glucan solution was able to induce arthritis when injected without IFA.
None of the LEW.1AV1 rats which were injected with IFA (incomplete Freund's adjuvant) developed arthritis whereas only 17% of (DA x LEW.1AV1)F1 , 46% of (DA x LEW.1AV1)F2 and 75% of DA x F1 developed arthritis.
These are susceptible to collagen-induced arthritis whereas common LEW rats are not. They develop less severe arthritis 30 days after immunization with IFA, hence the arthritis score late in disease is higher than the DA rats.