Since the biologic function of the HLA molecules is presenting endogenous and exogenous antigens, they manifested high structural polymorphism. HLA presents the highest degree of polymorhism is due to gene conversion between variable alleles and loci within each HLA gene. The number of HLA allele’s increase at a regular rate, about 15% of the alleles in the high-expression loci (A,B,C and DRB1) and 30% in the low expression loci (DRB3/4/5, DQB1, DPB1)are truly relevant in clinical typing. The number of alleles will keep growing. The number of variant alleles at class I and class II loci according to the IMGT-HLA database.