Bufo MHC class II loci with conserved introns flanking exon 2: cross-species amplification with common primers

We characterized the complete second exon with adjacent introns of MHC class II beta genes in the anurans Bufo calamita, B. bufo and B. viridis. Introns were remarkably conserved among species. There were at least two loci (A and B), which we amplified with different forward primers but identical reverse primers. Locus A had low diversity whereas locus B exhibited 42 alleles in B. calamita and 14 in B. bufo. We detected evidence of positive selection at antigen binding sites in both these species and demonstrated expression of locus B in B. calamita.