Received 8/5/97 Accepted 8/12/97

Mycobacterial infections have afflicted humanity since early recorded time. Perhaps, the best known mycobacterial infections are tuberculosis and leprosy. In recent years, another group of mycobacteria has become important in the development of human disease. Soon after medical science became aware of the human immunodeficiency virus (HIV), it was realized that an opportunistic group of mycobacteria, the Mycobacterium avium complex, played a major role in the progression and outcome of that viral disease. Since the early 1980's the M. avium complex has made an important contribution to the progression of AIDS. Historically M. avium has not played a major role as a human pathogen. As discussed previously (1), M. avium pathogenicity probably results from several contributing factors. Normally (i.e., immunocompetent host), only subclinical infections result. However, in an immunodeficient host (e.g., HIV-infected individual) the effects of these contributing factors can be critical, resulting in loss of effective host response. Thus, under the right conditions, an opportunistic pathogen such as M. avium can progress to the higher level of 'pathogen', and create conditions that result in higher mortality rates. For M. avium, this generally occurs when the patient's CD4+ population of T-lymphocytes is reduced to a level below 100 mm² (2, 3).

It is interesting to note that M. avium is the primary mycobacterial infection observed in advanced stages of AIDS, even though there are other ubiquitous opportunistic mycobacterial species that can potentially co-infect AIDS patients. Reportedly, 50-70% of patients in the advanced stages of AIDS have M. avium infections (2, 4, 5). To understand why M. avium has the potential to manifest itself as a 'pathogen', and contribute to advanced stages of AIDS, it becomes important to understand the organism with regard to the various lipids associated with its growth and persistence in a host.

The purpose of this review, therefore, will be to examine the processing of mycobacterial lipids with an attempt to better understand how these events affect the immune responsiveness of the infected host. Because numerous articles have addressed the pathogenic aspects of other mycobacteria, such as M. tuberculosis and M. leprae, the primary focus of this review will be M. avium and its contribution to advanced stages of AIDS.