Genetic Differentiation in a Sample from Northern Mexico City Detected by HLA System Analysis: Impact in the Study of Population Immunogenetics

The major histocompatibility complex is directly involved in the immune response, and thus the genes coding for its proteins are useful markers for the study of genetic diversity, susceptibility to disease (autoimmunity and infections), transplant medicine, and pharmacogenetics, among others. The polymorphism of the system also allows researchers to use it as a proxy for population genetics analysis, such as genetic admixture and genetic structure. In order to determine the immunogenetic characteristics of a sample from the northern part of Mexico City and to use them to analyze the genetic differentiation from other admixed populations, including those from previous studies of Mexico City population, we analyzed molecular typing results of donors and patients from the Histocompatibility Laboratory of the Central Blood Bank of the Centro Médico Nacional La Raza selected according to their geographic origin. HLA-A, -B, -DRB1, and -DQB1 alleles were typed by polymerase chain reaction with sequence-specific primers. Allelic and haplotype frequencies, as well as population genetics parameters, were obtained by maximum likelihood methods. The most frequent haplotypes found were HLA-A^*02/-B^*39/-DRB1^*04/-DQB1^*03:02P, HLA-A^*02/-B^*35/-DRB1^*04/-DQB1^*03:02P, HLA-A^*68/-B^*39/-DRB1^*04/-DQB1^*03:02P, and HLA-A^*02/-B^*35/-DRB1^*08/-DQB1^*04. Importantly, the second most frequent haplotype found in our sample (HLA-A^*02/-B^*35/-DRB1^*04/-DQB1^*03:02P) has not been previously reported in any mixedancestry populations from Mexico but is commonly encountered in Native American human groups, which can reflect the impact of migration dynamics in the genetic conformation of the northern part of Mexico City, and the limitations of previous studies with regard to the genetic diversity of the analyzed groups. Differences found in haplotype frequencies demonstrated that large urban conglomerates cannot be analyzed as one homogeneous entity but, rather, should be understood as a set of structures in which social, political, and economical factors influence their genesis and dynamics.