HLA: Facts and Findings

Abstract

Human Major Histocompatibility Complex also known as Human Leukocyte Antigen (HLA) system is an extended portion of human genome spanning a region of about 4000 Kb on the short arm of chromosome 6 between 6p21.31 and 6p21.32.1. This region contains a large number of polymorphic genes with variable expression and function which are arranged close together and are generally inherited as a haplotype. These genes have been grouped into different clusters based on their structural and functional characteristics namely: Class I, II and III. Due to their diploid nature, an individual inherits two alleles of each HLA loci, one each from either parent. Furthermore, due to very low recombination frequency (less than 1%), a complete set of alleles on the same chromosome is usually inherited as a haplotype. Approximately 150 billion or even more genotypic combinations are possible in the HLA system. According to Klein, such a polymorphism is not only advantageous for an individual, but also enhances the survivality of the species surrounded by plethora of pathogens.