Experimental Mycobacterium tuberculosis infection of cynomolgus macaques closely resembles the various manifestations of human M. tuberculosis infection

Abstract

Nonhuman primates were used to develop an animal model that closely mimics human Mycobacterium tuberculosis infection. Cynomolgus macaques were infected with low doses of virulent M. tuberculosis via bronchoscopic instillation into the lung. All monkeys were successfully infected, based on tuberculin skin test conversion and peripheral immune responses to M. tuberculosis antigens. Progression of infection in the 17 monkeys studied was variable. Active-chronic infection, observed in 50 to 60% of monkeys, was characterized by clear signs of infection or disease on serial thoracic radiographs and in other tests and was typified by eventual progression to advanced disease. Approximately 40% of monkeys did not progress to disease in the 15 to 20 months of study, although they were clearly infected initially. These monkeys had clinical characteristics of latent tuberculosis in humans. Low-dose infection of cynomolgus macaques appears to represent the full spectrum of human M. tuberculosis infection and will be an excellent model for the study of pathogenesis and immunology of this infection. In addition, this model will provide an opportunity to study the latent M. tuberculosis infection observed in approximately 90% of all infected humans.

FIG. 1.

Tuberculin skin testing results convert to positive shortly after infection with M. tuberculosis but are variable throughout the course of infection. Monkeys were injected with 0.1 ml of mammalian tuberculin in the right or left palpebral site or on the abdomen, and the test result was graded from 0 to 5 (for eyelid) or induration was measured on the abdomen in millimeters at 48 and 72 h. Reported here are the 72-h readings for six representative monkeys tested at various time intervals postinfection. Monkey numbers are shown beside symbols on the graph.

FIG. 2.

Chest radiographs from monkeys infected with M. tuberculosis. The right side of the monkey is marked on radiographs as “R.” (A to C) Monkey 152-00. (A) Four weeks postinfection; note the presence of infiltrate in right lobes (arrows). (B) Seven months postinfection; evidence of disease in right lobes still apparent (arrow). (C) Eleven months postinfection; negative radiograph indicating resolution of disease. (D) Monkey 153-00, rapidly progressing disease, involvement of both left and right sides of lung at 10 weeks postinfection (time of necropsy).

FIG. 3.

Lung granulomas from monkeys with active-chronic disease. (A) Granuloma with central caseation from monkey with rapid, progressive disease (153-00). The caseation is surrounded by epithelioid macrophages, and the presence of neutrophils and peripheral lymphocytes is noted. (B) Granuloma from monkey with active-chronic disease, necropsied before progression to advanced disease (151-00). This is an example of a solid granuloma, without central caseation, and shows the presence of multinucleated giant cells, as well as substantial lymphocytic infiltration. Magnifications, ×190. All tissues were stained with H&E.

FIG. 4.

Granulomas from monkeys with resolving or latent infection. Overall, the granulomas had fewer epithelioid macrophages and giant cells. (A) Mineralization (confirmed as calcification by von Kossa staining [data not shown]) of central caseous material of lung granuloma from a monkey with resolving lung disease (152-00). Magnification, ×196. (B) From monkey 146-00 (apparent latent infection), right hilar lymph node section showing extensive nodal effacement with caseous necrosis and focal areas of early mineralization. Magnification, ×98. (C) Lung granuloma from monkey 146-00, with less caseation than in more advanced monkeys, and development of progressive, dense fibrous connective tissues and reduced lymphocytic infiltration, consistent with containment of infection. Magnification, ×19.6. (D) Higher-power magnification (×196) of dense, organized fibrotic tissue surrounding granuloma. All tissues were stained with H&E.