Mycobacterium avium-intracellulare complex infections in the acquired immunodeficiency syndrome

Intramacrophagic Mycobacterium avium bacilli are coated by a multiple lamellar structure: freeze fracture analysis of infected mouse liver

We used freeze fracture electron microscopy to study the fine structure of Mycobacterium avium inside phagosomes of murine macrophages. M. avium-susceptible C57BL/6 mice were infected with M. avium by intraperitoneal inoculation of 10(8) viable bacilli. We studied the microanatomy of the mycobacteria in 3-month infections of mice, a situation in which bacillary multiplication is extensive. In these samples, freeze fracture revealed that intraphagosomal bacilli were surrounded by a multilamellar coat that was apposed to the cell wall. In thin sections, in contrast, the area corresponding to the coat showed no substructure and was electron transparent (the so-called electron-transparent zone that has been previously reported by others). The multiple lamellae resembled an onionlike assembly that was inserted in between the mycobacterial wall outer surface and the phagosomal membrane. Each lamella of the M. avium coat was made up of parallel straight fibrils with a width of 5 nm. A variable number of lamellae, sometimes up to 10 or more elements, coated individual bacilli. The multilamellar coat was absent around both extracellular M. avium and intramacrophagic M. avium after short-term (45-min) inoculation of mice. The supramolecular organization of the M. avium lamellar coat as viewed here by freeze fracture is similar to that of purified mycoside C (P. Draper, J. Gen. Microbiol. 83:431-433, 1974; K.-S. Kim, M.R.J. Salton, and L. Barksdale, J. Bacteriol. 125:739-743, 1976), a mycobacterial component currently known as glycopeptidolipid (W.W. Barrow and P.J. Brennan, J. Bacteriol. 150:381-384, 1982). We conclude that M. avium bacilli growing in macrophages are surrounded by multilamellar capsulelike structures that contain glycopeptidolipid molecules.

The carbohydrate- and lipid-containing cell wall of mycobacteria, phenolic glycolipids: structure and immunological properties

Phenolic glycolipids were first discovered as cell-wall constituents of M. bovis, M. bovis BCG, M. marinum, and M. kansasii. Recently, such compounds were also isolated from M. leprae and have been shown to be specific-species serological markers. Moreover, they seem to be involved, in the case of lepromatous leprosy, in the stimulation of the suppressor T-cells. The functional activities of these phenolic glycolipids over the immune cells stimulation emphasized the role played by these molecules in the mycobacteria pathogenicity. Phenolic glycolipids have also been found in M. gastri and M. tuberculosis strain Canetti. From a structural point of view, these glycolipids contain the same aglycon moiety mainly assigned to phenolphthiocerol diester while the sugar part structure confers to some of these glycolipids their antigenic specificity. The search of immunoreactive glycolipids and their function analysis remain a challenge for chemists and immunologists for the understanding of the mycobacteria pathogenicity.

Defects in sera from acquired immunodeficiency syndrome (AIDS) patients and from non-AIDS patients with Mycobacterium avium infection which decrease macrophage resistance to M. avium

Some characteristics of the sera and macrophages (MP) of human immunodeficiency virus (HIV)-infected patients which might contribute to their unusual susceptibility to Mycobacterium avium infection were studied. Cultures of patient peripheral blood MP in medium supplemented with their sera or normal subject sera were infected with M. avium and compared with similar cultures of normal MP. Intracellular mycobacterial replication was measured in the infected MP by CFU counts of the bacteria made from lysed samples of the MP at 0, 4, and 7 days after MP infection. Sera from patients with chronic granulomatous infection with M. avium, but no HIV infection, also were studied. The sera from all of the patients with chronic granulomatous infection and from several HIV-infected patients were deficient or lacking in an inhibitor that in normal serum acts within normal MP to suppress intracellular growth of M. avium. Most of the HIV-infected patients also had MP that were abnormally permissive for M. avium because they responded poorly to the serum inhibitor. Elucidation of these associated defects in native defenses against M. avium may result in better prevention and therapy of M. avium infections.