HLA Typing at the DNA Level

As HLA alleles are defined biologically by their nucleotide sequences, there is an obvious logic in typing for alleles using methods that directly assess DNA sequences rather than the structures of the proteins they encode. In one type of method 2 the polymorphic exon 2 of the targeted class II gene is amplified using PCR. The amplified DNA is then covalently attached to a nylon membrane by ultraviolet irradiation and incubated with an oligonucleotide designed to detect a particular polymorphic motif and modified, so that it can be detected when bound to the membrane. This chapter explores the methods for typing of genomic DNA, and for distinguishing various alleles, these methods have been successfully used for class II typing. A major consequence of the application of DNA typing is that it has led to the discovery and characterization of many new alleles. Most new HLA alleles arise by genetic events that recombine substitutions in the existing alleles.