Abstract:

Objective: By constructing animal infection models of Xinjiang Mycobacterium tuberculosis (MTB) CAS lineage and H37Rv standard strain, to systematically investigate the changes of core indicators such as MTB growth in organs of infected mice, tissue pathological damage, and immune response, and to reveal the unique virulence characteristics of the CAS lineage, laying a data foundation for subsequent vaccine development, drug susceptibility assessment, and clinical treatment strategy development targeting the CAS lineage. Methods: Mice were placed in IVC cages for one week to observe and exclude abnormal ones. Then, 30 mice were randomly divided into three groups with 10 in each group, then they were injected with 0.2 ml (1×10⁷ CFU/ml) bacterial suspension with H37Rv standard strain, Xinjiang CAS lineage clinical isolates, and the same dose of normal saline via tail vein respectively. At the 4th and 8th weeks after infection, half of the mice in each group were sacrificed by cervical dislocation after collecting 0.8-1 ml of blood from their eyeball. The lung, spleen, liver, and kidney tissues were ground and divided into two pieces. One piece was used for culturing to observe the growth of MTB, and the other piece was fixed for tissue sectioning to observe their pathological changes. The eyeball serum samples were used for immunological examination. Results: In terms of MTB culture of organ tissues, the positive rate of H37Rv standard strain was significantly higher than that of the CAS lineage clinical isolates (70.0% (7/10) vs. 0.0% (0/10), Fisher’s exact test, P=0.003). In terms of serum immunoglobulins, in the early stage of infection (4th week), the levels of IgM and IgA in the CAS group ((0.95±0.19) mg/ml and (1.50±0.42)×10^-2 mg/ml) were higher than those in the H37Rv group (0.71 (0.38, 0.80) mg/ml and 0.56×10^-2 (0.10×10^-2, 0.81×10^-2) mg/ml) and the normal saline group ((0.50±0.13) mg/ml and 0.28×10^-2 (0.21×10^-2, 0.51×10^-2) mg/ml), and the differences were statistically significant (t=-2.634, P=0.022; t=2.951, P=0.012; t=-3.921, P=0.002; t=-4.526, P=0.001). In the later stage of infection (8th week), the levels of IgG, IgM, and IgA in the H37Rv group ((6.88±1.80) mg/ml, (0.92±0.16) mg/ml, (1.32±0.59)×10^-2 mg/ml) were higher than those in the normal saline group (3.83 (2.12, 5.04) mg/ml, (0.61±0.09) mg/ml, (0.39±0.14)×10^-2 mg/ml), and the levels of IgG and IgA in the CAS group ((7.26±1.64) mg/ml and (0.92±0.32)×10^-2 mg/ml) were significantly higher than those in the normal saline group (t=-3.827, P=0.002; t=-3.738, P=0.003; t=-2.573, P=0.024; t=4.403, P=0.001; t=2.902, P=0.013). In terms of pathological changes, both the H37Rv group and the CAS group showed obvious signs of tuberculosis infection in lung tissue, characterized by local diffuse congestion and hemorrhage, alveolar septum thickening, lymphocytes and monocytes infiltration, occasional scattered foam cells, and bronchiectasis. Moreover, the pathological changes were more severe at the 8th week than at the 4th week, and the H37Rv group was slightly more severe than the CAS group. Conclusion: This study successfully established mouse models infected with the H37Rv standard strain and the Xinjiang CAS lineage clinical isolates. The results indicated that mice showed significantly stronger anti-inflammatory ability against the Xinjiang CAS lineage clinical isolates than against the H37Rv standard strain.

Key words: Mycobacterium tuberculosis, Pedigree, Disease models, animal, Mice, Xinjiang