MAPPING OF SUSCEPTIBILITY TO MAREKS-DISEASE WITHIN THE MAJOR HISTOCOMPATIBILITY (B)-COMPLEX BY REFINED TYPING OF WHITE LEGHORN CHICKENS

The major histocompatibility (B) complex of a distinct commercial pure White Leghorn chicken line was characterized using serological, bioch emical and restriction fragment length polymorphism (RFLP) typing. Lin e B chickens displayed a high recombination frequency within the B com plex. Three recombinant haplotypes were identified. The influence of t hese haplotypes was determined in relation to the haplotypes B19 and B 21 on their resistance to Marek's disease (MD) in an experimental infe ction with the virus. Offspring of sires with a recombinant haplotype in combination with B19 or B21, and dams, which were homozygous B19/B1 9 or B21/B21 were infected. The B type of the offspring had a signific ant effect upon survival. Animals with B complex types B21/B21, B134/B 21 and B234/B21 were relatively resistant to MD (24-32% mortality), wh ereas B19/B19 birds were highly susceptible (68% mortality). Animals w ith a recombinant halpotype B19r21 (B-G21, B-F19) were equally suscept ible to MD as birds with the complete B19 haplotype. In contrast to ea rlier publications, resistance was not inherited as a dominant trait. Apparently, B19 was associated with a dominant susceptibility. The gen e(s) associated with the B complex and involved in resistance to MD we re localized within the B-F/B-L region. However, the association with a presumably non-coding subregion of B-G could not be excluded.