Identification of New World monkey MHC-DRB alleles using PCR, DGGE and direct sequencing.

Identification of New World monkey MHC-DRB alleles has previously relied upon labor-intensive cloning and sequencing techniques. Here we describe a rapid and unambiguous way to distinguish DRB alleles in New World monkeys using the polymerase chain reaction (PCR), denaturing gradient gel electrophoresis (DGGE), and direct sequencing. The highly variable second exon of New World monkey DRB alleles was amplified using generic DRB primers and alleles were separated by DGGE. DNA was then reamplified from plugs removed from the gel and alleles were determined using fluorescent-based sequencing. The validity of this typing procedure was confirmed by the identification of all DRB alleles previously characterized by cloning and sequencing techniques from an individual cotton-top tamarin. Importantly, our analysis revealed DRB alleles not previously identified in this reference animal. Following validation of our technique, the protocol was employed for the characterization of MHC-DRB alleles in four other species of New World monkey: the pygmy marmoset, white-faced saki monkey, long-haired spider monkey and owl monkey. Using this technique, we identified five alleles from the cotton-top tamarin, five alleles from the owl monkey, three alleles from the long-haired spider monkey, three alleles from the white-faced saki monkey and two alleles from the pygmy marmoset. On the basis of phylogenetic tree analyses, 13 new DRB alleles were assigned to eight different MHC-DRB lineages. Whereas traditional DRB typing via cloning and sequencing provides limited information, our new technique provides a simple and relatively rapid way of identifying New World monkey MHC-DRB alleles.