Mycobacterium avium complex disease in patients with AIDS: seroreactivity to native and recombinant mycobacterial antigens

Application of a commercial serodiagnostic kit that measures the serum anti-glycopeptidolipid core IgA antibody in Mycobacterium avium complex pulmonary disease

The diagnosis of Mycobacterium avium complex (MAC) pulmonary disease is occasionally cumbersome and time-consuming because the MAC species is ubiquitous, and therefore its detection is not necessarily indicative of a definitive diagnosis. A serodiagnostic method specific for MAC pulmonary disease that measures the serum anti-glycopeptidolipid core antigen IgA has been developed and is commercially available. Meta-analysis revealed that the test showed a good diagnostic accuracy. The estimated sensitivity and specificity values were 69.6% (95% confidence interval 62.1-76.1) and 90.6% (95% confidence interval 83.6-95.1), respectively. As antibody levels may reflect the disease activity, their serial measurement can also be used in the management of MAC disease. To justify its routine use in clinical practice, further validation in various regions and studies addressing whether serodiagnosis combined with present diagnostic criteria facilitate more rapid accurate diagnosis of MAC pulmonary disease are necessary.

Identification, molecular cloning, and evaluation of potential use of isocitrate dehydrogenase II of Mycobacterium bovis BCG in serodiagnosis of tuberculosis

Diagnosis of tuberculosis is time-consuming and requires infrastructures which are often not available in countries with high incidences of the disease. In the present study, an 82-kDa protein antigen was isolated by affinity chromatography and was identified by peptide mass fingerprinting as isocitrate dehydrogenase II, which is encoded by the icd2 gene of Mycobacterium bovis BCG. The icd2 gene of BCG was cloned by PCR, and the product of recombinant gene expression was purified and analyzed by two-dimensional polyacrylamide gel electrophoresis. The recombinant protein, named rICD2, was tested for its recognition by immunoglobulin G (IgG) antibodies from the sera of 16 patients with tuberculosis (TB) and 23 healthy individuals by Western blotting. The results showed that rICD2 is recognized by IgG antibodies from the sera of all TB patients tested at serum dilutions of > or = 1:640. At a serum dilution of 1:1,280, the sensitivity was 50% and the specificity was 86.9%. These results indicate that rICD2 might represent a candidate for use in a new assay for the serodiagnosis of TB.

Protection against virulent Mycobacterium avium infection following DNA vaccination with the 35-kilodalton antigen is accompanied by induction of gamma interferon-secreting CD4(+) T cells

Mycobacterium avium is an opportunistic pathogen that primarily infects immunocompromised individuals, although the frequency of M. avium infection is also increasing in the immunocompetent population. The antigen repertoire of M. avium varies from that of Mycobacterium tuberculosis, with the immunodominant 35-kDa protein being present in M. avium and Mycobacterium leprae but not in members of the M. tuberculosis complex. Here we show that a DNA vector encoding this M. avium 35-kDa antigen (DNA-35) induces protective immunity against virulent M. avium infection, and this protective effect persists over 14 weeks of infection. In C57BL/6 mice, DNA vaccines expressing the 35-kDa protein as a cytoplasmic or secreted protein, both induced strong T-cell gamma interferon (IFN-gamma) and humoral immune responses. Furthermore, the antibody response was to conformational determinants, confirming that the vector-encoded protein had adopted the native conformation. DNA-35 immunization resulted in an increased activated/memory CD4(+) T-cell response, with an accumulation of CD4(+) CD44(hi) CD45RB(lo) T cells and an increase in antigen-specific IFN-gamma production. The protective effect of the DNA-35 vectors against M. avium infection was comparable to that of vaccination with Mycobacterium bovis BCG and significantly greater than that for previous treated infection with M. avium. These results illustrate the importance of the 35-kDa protein in the protective response to M. avium infection and indicate that DNA vaccination successfully promotes a sustained level of protection during chronic M. avium infection.

Serum antibody reactivity to recombinant mig and whole cell antigens in Mycobacterium avium infection

Mycobacterium avium is a significant opportunistic pathogen in immunocompromised patients. Moreover, the prevalence of infections in patients without known predisposing conditions has also been increasing in recent years. Patients would greatly benefit from early diagnosis of disseminated infection. Serodiagnostic tests have already been promising in tuberculosis and immunocompetent patients but studies in HIV-infected patients and humoral response to M. avium antigens resulted in conflicting data. We have evaluated the use of the phagocytosis-induced MIG protein of M. avium as a diagnostic antigen. Serum antibody levels of M. avium-infected, HIV-negative patients were significantly elevated for the recombinant MIG (p < 0.001) and also for M. avium whole-cell antigens (p < 0.025) as compared to controls. In contrast, HIV-infected patients with disseminated M. avium infection demonstrated also elevated levels of antibody for the whole-cell antigen (p < 0.00001) but a decreased reactivity for the MIG antigen (p < 0.007). The recombinant antigen proved to have no cross-reactivity with M. tuberculosis antigens as antibody levels were decreased in tuberculosis patients (p < 0.001). Therefore, a simultaneous serological test using recombinant MIG and the whole cell antigens might be helpful in the sometimes problematic diagnosis of M. avium infections in patients without predisposing conditions.

Age-dependent humoral responses of children to mycobacterial antigens

In the United States, disseminated infection with environmental mycobacteria, including the Mycobacterium avium complex, is the most common opportunistic bacterial infection seen in AIDS patients. However, the source and relative degree of exposure to environmental mycobacteria during childhood are unknown. To examine the age-related exposure to mycobacteria, we obtained serum samples from 150 children ranging in age from 6 months to 18 years. Each sample was tested against both M. avium (serovar 1) sonic extracts and mycobacterial lipoarabinomannan, using an enzyme-linked immunosorbent assay (ELISA). All serum samples were also subjected to immunoblot analysis with the sonic extract antigen. These studies established that elevated ELISA values (P < 0.0001) and increased immunoblot reactivity (P < 0.0001) against mycobacterial antigens were both associated with increasing age. The seroreactivity differences were most striking when comparing the age groups of children below the age of 6 with the older age groups. Our results suggest that the development of humoral immune responses to mycobacterial antigens in children correlates with increasing age and that there may be an environmental factor predisposing to mycobacterial exposure which is related to advancing age.

Six years' experience with the discontinuation of BCG vaccination. 4. Protective effect of BCG vaccination against the Mycobacterium avium intracellulare complex

SETTING

In 1986, mass BCG vaccination of newborns was discontinued in an extensive territorial sample of neonates in the Czech Republic (30,000 infants annually). The non-vaccinated children have since been tuberculin tested at two-year intervals; those with continual or repeated intensive contact with animals in households or on farms were also tested with Mycobacterium avium intracellulare complex sensitin in addition to tuberculin.

OBJECTIVE

Within the frame work of the surveillance programme the incidence of infection and disease caused by M. avium intracellulare complex (M. avium complex) was evaluated and the protective effect of BCG vaccination analysed.

DESIGN

In 1986-93, out of 190,874 non-vaccinated children, 36 were found to be infected by M. avium complex; 27 of them developed disease, i.e. mycobacteriosis other than tuberculosis (MOTT).

RESULTS

The annual risk of infection with M. avium complex was 4.8/100,000 children per year, of whom 3.6/100,000 developed mycobacteriosis. 24 patients suffered from swelling of cervical lymph nodes, 2 of mediastinal lymph nodes and one child had the disease localized both in cervical and mediastinal lymph nodes. The disease was verified bacteriologically in 9 children. Most of the diseased children had impaired immunity; a marked skin reactivity of M. avium complex sensitin was present in all infected children. Animal sources infected by M. avium complex were detected in 5 cases. Another 14 children also had close contact with animals but without proven M. avium complex infection.

CONCLUSION

In non-BCG vaccinated children the incidence of lymphadenitis caused by M. avium complex was considerably higher than in vaccinated children. BCG cells possess antigenic determinants which confer protective immunity probably both against M. tuberculosis and against M. avium complex infections. It may thus be assumed that BCG vaccination protects both against pathogenic tubercle bacilli and M. avium complex. This should be taken into consideration before recommending discontinuation of mass BCG vaccination of newborns in areas with a high prevalence of M. avium complex infection.

Rapid detection and identification of Mycobacterium avium by amplification of 16S rRNA sequences

An assay that is based on the amplification of 16S rRNA sequences and that was initially developed to detect Mycobacterium paratuberculosis in cattle was used to test 20 serotypes of the Mycobacterium avium complex (MAC) and atypical mycobacterial species not belonging to MAC. Only serotypes 1 to 6 and 8 to 11, designated M. avium, were detected by the assay, indicating that it can be used for the rapid detection and identification of M. avium. The results of the assay for clinical samples from animals suspected of having mycobacterial infections indicated that it can also be used directly on clinical samples.

The Mycobacterium avium complex

Mycobacterium avium complex (MAC) disease emerged early in the epidemic of AIDS as one of the common opportunistic infections afflicting human immunodeficiency virus-infected patients. However, only over the past few years has a consensus developed about its significance to the morbidity and mortality of AIDS. M. avium was well known to mycobacteriologists decades before AIDS, and the MAC was known to cause disease, albeit uncommon, in humans and animals. The early interest in the MAC provided a basis for an explosion of studies over the past 10 years largely in response to the role of the MAC in AIDS opportunistic infection. Molecular techniques have been applied to the epidemiology of MAC disease as well as to a better understanding of the genetics of antimicrobial resistance. The interaction of the MAC with the immune system is complex, and putative MAC virulence factors appear to have a direct effect on the components of cellular immunity, including the regulation of cytokine expression and function. There now is compelling evidence that disseminated MAC disease in humans contributes to both a decrease in the quality of life and survival. Disseminated disease most commonly develops late in the course of AIDS as the CD4 cells are depleted below a critical threshold, but new therapies for prophylaxis and treatment offer considerable promise. These new therapeutic modalities are likely to be useful in the treatment of other forms of MAC disease in patients without AIDS. The laboratory diagnosis of MAC disease has focused on the detection of mycobacteria in the blood and tissues, and although the existing methods are largely adequate, there is need for improvement. Indeed, the successful treatment of MAC disease clearly will require an early and rapid detection of the MAC in clinical specimens long before the establishment of the characteristic overwhelming infection of bone marrow, liver, spleen, and other tissue. Also, a standard method of susceptibility testing is of increasing interest and importance as new effective antimicrobial agents are identified and evaluated. Antimicrobial resistance has already emerged as an important problem, and methods for circumventing resistance that use combination therapies are now being studied.

Nucleotide sequence analysis and serologic characterization of a 27-kilodalton Mycobacterium intracellulare lipoprotein

Disseminated mycobacteremia resulting from Mycobacterium avium-Mycobacterium intracellulare complex (MAC) infections frequently contribute to the morbidity and mortality seen in AIDS patients. To better understand the immunopathology of MAC disease and to identify molecules that may have potential diagnostic and vaccine utility, an immunoreactive M. intracellulare protein (MI43) and the gene encoding this antigen were characterized. Southern blot hybridizations demonstrated that MI43 gene probes reacted only with genomic DNA from M. intracellulare, M. avium, and Mycobacterium asiaticum and not with DNA isolated from 11 other mycobacterial species. Nucleotide sequence analysis showed that the MI43 gene encodes a 27-kDa protein which contains a consensus bacterial lipoprotein processing sequence. Detergent-phase separations and metabolic labeling with [3H]palmitate also suggested that MI43 is a lipoprotein. Serological assays demonstrated that recombinant MI43 fusion proteins react with sera from M. avium-infected mice, sera from patients with MAC disease, and sera from patients with active tuberculosis. These results further suggest that mycobacterial lipoproteins are important immunogens that should be considered in the development of improved mycobacterial vaccines and diagnostic reagents.

Antigens of the Mycobacterium avium, Mycobacterium intracellulare complex

In the past decade, the clinical significance of the Mycobacterium avium, Myobacterium intracellulare complex (MAC) has increased dramatically primarily because of the association between the MAC and the acquired immunodeficiency syndrome (AIDS). Recent hospital reports have suggested that about one-half of AIDS patients in the United States are infected with the MAC. The resulting myobacteremia is a primary cause of mortality in 5-10% of these patients. This increased clinical importance of the MAC has generated renewed interest in MAC immunobiology. In this review, recent immunological and biochemical characterizations of four classes of dominant myobacterial antigens - glycopeptidolipids, arabinogalactan, lipoarabinomannan and MAC proteins - is examined. In addition, future prospects for improved diagnosis of MAC disease using defined monospecific antigens is discussed.