Effects of aminoguanidine on latent murine tuberculosis.

A unique feature of Mycobacterium tuberculosis is its ability to establish latent infection in the human host, which can reactivate to cause disease years later. In the present study, the mechanisms involved in the control of latent tuberculous infection were examined using two murine experimental tuberculosis models. Analysis of the model involving infection of mice with a relatively low inoculum of the virulent Erdman strain of M. tuberculosis indicated that in vivo inhibition of reactive nitrogen intermediate (RNI) production by the nitric oxide synthase inhibitor aminoguanidine resulted in reactivation. This reactivation was evidenced by hepatosplenomegaly, a robust tissue granulomatous reaction, and increased bacillary load. IFN-gamma, TNF-alpha, and inducible nitric oxide synthase were all expressed throughout the latent phase of infection. Reactivation of latent tuberculous infection by aminoguanidine treatment was confirmed using a second murine tuberculosis model based on treatment with antimycobacterial drugs. Results obtained using this drug-based model also suggested the existence of an RNI-independent antimycobacterial mechanism(s) operative in the latent phase of infection. Together, these data suggest that both RNI-dependent and -independent mechanisms contribute to the prevention of tuberculous reactivation.