Mycobacterium avium Complex Pulmonary Disease in Immunocompetent Patients

Use of mefloquine in multidrug-resistant Mycobacterium avium complex pulmonary disease in an HIV-negative patient

INTRODUCTION

Mycobacterium avium complex (MAC) is a leading cause of pulmonary disease (PD), even in those with intact immunity, representing about 30% of the cases of pleuropulmonary mycobacterial infection. Based on previous studies, macrolides are the only agents used in the treatment of MAC disease for which there is a correlation between in vitro susceptibility and in vivo (clinical) response. However, resistance develops rapidly if single-agent treatment is used. Data regarding treatment of macrolide-resistant MAC (MRMAC) and multidrug-resistant MAC (MDRMAC) are sparse.

CASE SUMMARY

A 50-year-old, HIV-negative white man, weighing 53.6 kg, with severe chronic obstructive pulmonary disease and bronchiectasis was initially on treatment for MAC-PD and MRMAC. The patient was followed between 1999 and 2006. His treatment history revealed that in addition to the multiple drugs administered during the course of his illness, thalidomide, interferon-γ, and mefloquine were also administered. The patient died ~7 years later due to respiratory failure and overwhelming infection

CONCLUSIONS

This case report describes the use of mefloquine as adjunct treatment in an HIV-negative patient with MDRMAC-PD and discusses the associated outcomes of drug resistance.

Mycobacterium avium-induced SOCS contributes to resistance to IFN-gamma-mediated mycobactericidal activity in human macrophages

Mycobacterium avium is an opportunistic pathogen that commonly infects individuals colonized with HIV-1, although it is less frequent in the post-HAART era. These microorganisms invade macrophages after interacting with TLR2 and/or CD14 co-receptors, but signaling pathways promoting survival in macrophages are not well defined. Although IFN-gamma plays an important role in protective immunity against bacterial infections, IFN-gamma responses are compromised in AIDS patients and evidence suggests that exogenous IFN-gamma is inadequate to clear the mycobacteria. To determine the mechanism by which M. avium survives intracellularly, even in the presence of IFN-gamma, we studied the effect of mycobacteria infection in macrophages during early IFN-gamma signaling events. M. avium infected cells exhibited a reduced response to IFN-gamma, with suppressed phosphorylation of STAT-1 compared with uninfected cells. Interaction of M. avium with macrophage receptors increased gene expression of the suppressors of cytokine signaling (SOCS) to diminish IFN responsiveness. Specifically, we observed an increase in mRNA for both SOCS-3 and SOCS-1, which correlates with elevated levels of SOCS protein and positive immunostaining in M. avium/HIV-1 co-infected tissues. We also linked the p38 MAPK signaling pathway to mycobacterial-induced SOCS gene transcription. The induction of SOCS may be part of the strategy that allows the invader to render the macrophages unresponsive to IFN-gamma, which otherwise promotes clearance of the infection. Our data provide new insights into the manipulation of the host response by this opportunistic pathogen and the potential for modulating SOCS to influence the outcome of M. avium infection in immunocompromised hosts.