A molecular biology approach to tuberculosis

Isolation and characterization of the major histocompatibility complex DQA1 and DQA2 genes in gayal (Bos frontalis)

The species origin of Yunnan gayal has been controversial since many years. However, few recent genetic studies have suggested that it has perhaps originated from the hybridization between male Bos frontalis and female B. taurus or B. indicus. Being an important semi-wild bovid species, this has also been listed under the red list of International Union of Conservation of Nature and Natural Resources. However, there is limited information available about the immunogenicity of this precarious species of Bos. Major histocompatibility complex (MHC) plays a pivotal role in immune response to infectious diseases in vertebrates. In the present study, we have investigated the structural and functional characteristics and possible duplication of the MHC-DQA genes in gayal (B. frontalis). Two full-length cDNA clones of the MHC-DQA genes were amplified and designated as Bofr-DQA1 (DQA*0101) and Bofr-DQA2 (DQA*2001) with GenBank accession numbers KT318732 and KT318733, respectively. A comparison between Bofr-DQA1, Bofr-DQA2 and to other MHC-DQA molecules from different animal species showed that nucleotide and encoded amino acid sequences of these two identifiedMHC-DQA genes have more similarity to alleles of specific DQA1 and DQA2 molecules from other Ruminantia species than to each other. The phylogenic investigation also demonstrated a large genetic distance between these two genes than to homologous from the other species. The large genetic distance between Bofr-DQA1 and Bofr-DQA2, and the presence of different bovine DQA putative motifs clarify that these sequences are nonallelic type. These results could suggest thatduplication of the DQA genes has also occurred in gayal. The findings of the present study have strengthened our understanding to MHC diversity in rare ruminants and mutation of immunological functions, selective and evolutionary forces that affect MHC variation within and between species.

Molecular epidemiology of human cases of tuberculosis by Mycobacterium bovis in Mexico

The purpose of this study was to evaluate the role of Mycobacterium bovis in human cases of tuberculosis (TB) in an endemic area of the disease in cattle. Sputum, urine and other tissue samples were obtained from: (1) TB-symptomatic patients, (2) dairy farm workers and (3) abattoir workers. Samples of macroscopic lesions suspicious of TB were also obtained from cattle at slaughter in the same geographic area. A total of 562 human samples were collected: 255 from symptomatic patients, 218 from farm workers and 93 from abattoir workers. Samples were analysed by the bacillus acido-alcohol resitant (BAAR) and polymerase chain reaction (PCR) tests and cultured in Stonebrink and Löwenstein-Jensen. Spoligotyping was performed in all isolates obtained by culture and the DNA obtained by PCR. From the total number of human cases, 34 (6%) showed M. bovis spoligotype; eight spoligotypes from cattle showed an identical pattern to three spoligotypes from humans; a different set of spoligotypes from cattle (n = 8) had only one spacer difference to a set of spoligotypes from humans (n = 2). These results provide further evidence that infected cattle represent a risk to public health and support previous reports about the role of M. bovis in Mexican patients. There is no doubt that genotyping M. bovis isolates collected from cattle may have a substantial impact on our understanding of the epidemiology of TB.