Development, validation, and use of a semi-quantitative histopathologic scoring system for assessment of pulmonary pathology in Rhesus macaques experimentally infected with Mycobacterium tuberculosis
Mycobacterium tuberculosis (Mtb) remains the single largest infectious disease killer of man worldwide. The non-human primate (NHP) model, including the Indian Rhesus macaque, is particularly valuable for the study of this disease because they fully recapitulate the pathological and immunological responses, can be co-infected with Simian Immunodeficiency Virus to model lentivirus synergism, and provide ideal candidates to study novel vaccine and drug development. However, while much has been elucidated over the past centuries in regards to host immunity, bacterial responses, and granuloma formation, little remains known about histomorphologic differences between active tuberculosis (ATBI) and latent tuberculosis (ATBI) disease states. Differentiation between these disease states, in humans or in NHPs, is based on clinical parameters, and there are currently no established methods for detecting morphologic differences between these conditions at the microscopic level. The aim of this study was to develop and validate a novel approach for assessment of pulmonary pathology in Rhesus macaques experimentally-infected with M. tuberculosis alone or in the setting of SIV co-infection. Archival lung samples from experimentally-infected macaques were assessed by blinded pathologists to determine differences in a series of pathological parameters based on previous experiments. Interobserver agreement and repeatability was good between pathologists. Significant differences were observed in several pathology categories, with ATBI animals having a greater likelihood of increased alveolar macropahges, type II pneumocyte hyperplasia, perivasculitis, vasculitis/lymphangitis, and consolidation in comparison to LTBI animals. SIV co-infection increased the likelihood of perivasculitis and lymphangitis/vasculitis in both ATBI and LTBI animals. SIV co-infection also increased alveolar macrophages and type II pneumocyte hyperplasia in LTBI animals. Immunofluorescence was used to confirm the presence of Mtb bacilli within the perivascular inflammation. A similar grading system approach was used in 2 additional studies examining reactivation of ATBI in the setting of SIV coinfection unrelated to CD4+ T cell depletion and to evaluate pulmonary pathology changes in the setting of the use of an attenuated vaccine in SIV co-infected animals with similarly significant results. This grading scheme provides a valuable and desperately needed adjunctive assessment tool for evaluation of pulmonary pathology changes in the NHP model of pulmonary tuberculosis.