cDNA, cloning, and sequencing For all animals used in this study RNA was isolated from lymphoblastoid B-cells (Rneasy kit, Qiagen) and subjected to One-Step RT-PCR, as recommended by the supplier (Qiagen or Promega). The primers 5′MBS: AATTCATGGCGCCCCGAACCCTCCTCCTGC and 3′ MBS: CTAGACCACACAAGACAGTTGTCTCAG were used that anneal specifically to Mhc-B transcripts in macaques (Boyson et al. 1996) . Furthermore, for a subset of the animals the generic class I primers 5′ GGACTCA G A A T C T C C C C A G A C G C C G A G a n d 3 ′ TCTCAGTCCCTCACAAGGCAGCTGTC were used. The final elongation step was extended to 30 min to generate a 3′dA overhang. The RT-PCR products were cloned using the InsT/Aclone kit (Fermentas) or the PCR cloning kit (Qiagen). After transformation, 32 to 48 colonies were picked for plasmid isolation. Sequencing reactions were performed using the BigDye terminator cycle sequencing kit, and samples were run on an automated capillary sequencing system (Applied Biosystems Genetic Analyzer 3100).