A Marmoset Model for Mycobacterium avium Complex Pulmonary Disease

Rationale Mycobacterium avium complex, is the most common nontuberculous mycobacterial respiratory pathogen in humans. Disease mechanisms are poorly understood due to the absence of a reliable animal model for M. avium complex pulmonary disease. Objectives Assess the susceptibility, immunologic and histopathologic responses of the common marmoset ( Callithrix jacchus ) to M. avium complex pulmonary infection. Methods 7 adult female marmosets underwent endobronchial inoculation with 10 8 colonyforming units of M. intracellulare and were monitored for 30 or 60 days. Prior to infection, chest radiograph and serum cytokines were assessed; serum cytokines were also monitored weekly for 30 days. At sacrifice 30 days (3 animals) or 60 days (4 animals) after infection, chest radiograph, serum and bronchoalveolar lavage cytokines, histopathology, and cultures of the bronchoalveolar lavage, lungs, liver, and kidney were analyzed. Measurements and Main Results Five of seven animals (two at 30 days and three at 60 days of infection) had positive lung cultures for M. intracellulare . Extra-pulmonary cultures were positive in three animals. All animals appeared healthy throughout the study. All five animals with positive lung cultures had radiographic changes consistent with pneumonitis. At 30 days, those with M. intracellulare lung infection showed granulomatous inflammation while at 60 days there was less inflammatory change but bronchiectasis was noted. The cytokine response in the bronchoalveolar lavage fluid was uniformly greater in the animals with positive M. intracellulare cultures than those without a productive infection with greater levels at 30-days compared to 60-days. Similarly, serum cytokines were more elevated in the animals that had positive M. intracellulare cultures compared to those without a productive infection, peaking 14-21 days after inoculation. Conclusion Endobronchial instillation of M. intracellulare resulted in pulmonary mycobacterial infection in marmosets with a differential immune response, radiographic and histopathologic abnormalities, and an indolent course consistent with M. avium complex lung infection in humans.