Study of Mycobacterial Infections

The nontuberculous mycobacteria (NTM) are ubiquitous environmental organisms found in soil and water that rarely cause disease in humans. Since exposure to these organisms is universal and disease is rare, it can be concluded that normal host defenses are almost always sufficient to prevent infection. It follows that otherwise healthy individuals who develop disease must have abnormal susceptibility or immune defects that permit infection with nontubercuolous mycobacteria. The organisms that are most commonly encountered in clinical practice include Mycobacterium avium, and M. intracellulare \[collectively known as the M. avium complex (MAC)\], M. kansasii, M. fortuitum, M. abscessus, and M. chelonae. These organisms share significant structural and biochemical similarities with their more pathogenic relative, M. tuberculosis (MTB). Recognition of host factors that predispose or lead to NTM infection may have important implications for pathogenesis and therapeutic intervention, and may be applicable to the more virulent MTB. Identification of genetic or acquired susceptibility factors may lead to recognition of endogenous pathways that can be exploited therapeutically and to possible gene identification. Over the last two decades, three important observations have been made regarding the pathogenesis of nontuberculous mycobacterial infections. 1) In patients infected with HIV, nontuberculous mycobacterial infections often occur when the CD4+ T-lymphocyte number falls below 50/mm3. This suggested that specific T cell products or activities were required for mycobacterial resistance. 2) An association was noted between pulmonary nontuberculous mycobacterial infections and a particular body habitus, predominantly in post-menopausal women (pectus excavatum, scoliosis, mitral valve prolapse). 3) Multiple defects have been found involving the interferon gamma synthesis and use pathways in patients with disseminated nontuberculous mycobacterial infection without HIV, suggesting this is a critical pathway for host defense against these organisms. We seek to better characterize the predisposition to mycobacterial infection. This study will specifically address several aspects of immune function and investigate the proposed link to body morphotype in the relevant population. By collecting this information, we hope to provide insight into disease associations, infection susceptibility, and genetic predisposition to mycobacterial infection.