Antibodies to mycobacterial peptidoglycolipid and to crude protein antigens in sera from different categories of human subjects

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.

Serodiagnosis of pulmonary disease due to Mycobacterium avium complex with an enzyme immunoassay that uses a mixture of glycopeptidolipid antigens

It is difficult to distinguish pulmonary disease due to Mycobacterium avium complex (MAC) from that due to other mycobacteria, such as Mycobacterium tuberculosis and Mycobacterium kansasii. We developed an enzyme immunoassay (EIA) for diagnosis of MAC pulmonary diseases that uses glycopeptidolipid (GPL) antigens specific for MAC, and we used it for diagnosis in immunocompetent patients. The mean optical densities (+/- standard deviation) of serum immunoglobulin G antibodies to GPLs in patients with MAC disease, MAC colonization, M. kansasii disease, and tuberculosis and in healthy subjects were 0.778+/-0.784, 0.042+/-0.035, 0.059+/-0.035, 0.071+/-0.035, and 0.030+/-0.027, respectively. A significant increase in the level of anti-GPL antibodies was detected in patients with MAC disease. The level of anti-GPL antibodies reflected disease activity, because the level was decreased in culture-negative patients who had conversion of culture results. When a cutoff level of seropositivity (0.119) was defined, the sensitivity of EIA for diagnosis of MAC disease was 92.3%, and the specificity was 96.7%. Measurement of serum anti-GPL antibodies is useful for both the diagnosis of and assessment of activity in MAC disease.

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.

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.

Immunoglobulin A (IgA) and IgG serum antibodies to mycobacterial antigens in Crohn's disease patients and their relatives

Sera from patients with Crohn's disease, their relatives, their spouses, and unrelated healthy controls were assayed by enzyme-linked immunosorbent assay for immunoglobulin G (IgG) and IgA antibodies to Mycobacterium tuberculosis, M. avium, and M. gordonae. The patients had significantly higher IgA responses to mycobacterial antigens than did either their relatives or the controls. On the other hand, both the patients and their relatives had significantly higher IgG responses against these antigens than did the controls. The elevated IgA response was more pronounced against isopentanol-extracted whole bacterial cells than it was against soluble protein extracts, and it appeared to be directed against fixed surface antigens that lie under the loosely bound peptidoglycolipid or glycolipid antigens of mycobacteria.

Agents of newly recognized or infrequently encountered mycobacterial diseases

This paper reviews recent information on the systematics and clinical significance of potentially pathogenic environmental mycobacteria. A short history of these mycobacteria is given. Information on species for which clinical and systematic aspects have already been well documented, i.e., Mycobacterium kansasii, M. marinum, M. scrofulaceum, M. simiae, M. szulgai, M. ulcerans, M. xenopi, and members of the M. fortuitum complex, is updated. Although the M. avium complex was extensively reviewed in earlier literature, major new systematic and clinical information is presented in some detail. Species that have received very limited prior coverage, i.e., M. asiaticum, M. haemophilum, M. malmoense, and M. shimoidei, are the main subjects of this review and are discussed in detail. The rare infections attributed to species that are normally considered nonpathogenic, i.e., M. gastri, M. gordonae, the M. terrae complex, and most of the rapidly growing mycobacteria outside of the M. fortuitum complex, are critically reviewed. Finally, suggestions are offered for practical measures that can minimize the risk of failing to isolate or misidentifying some of the more obscure potentially pathogenic environmental mycobacteria that are only infrequently recognized.

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

Antibodies to Mycobacterium avium complex (MAC) antigens were measured by enzyme-linked immunosorbent assays and immunoblot analyses in sera from 20 patients with AIDS and disseminated MAC disease, 5 human immunodeficiency virus-seronegative patients with pulmonary MAC infections, and 20 healthy controls. Whereas enzyme-linked immunosorbent assay titers for healthy controls and patients with AIDS and MAC disease were comparable, human immunodeficiency virus-seronegative patients with MAC disease had higher anti-MAC antibody titers (P less than 0.01). Immunoblot analysis with the same sonic extracts indicated that each of the three groups had a limited heterogeneous response to M. avium antigens. No significant differences in immunoblot reactivities were detected. However, immunoblot studies with recombinant nontuberculous mycobacterial antigens revealed that sera from over 90% of the patients with MAC disease and only 25% of controls recognized a recombinant protein derived from a 35-kDa mycobacterial antigen. Although sonic extracts did not permit adequate discrimination of antibody reactivity in patients with MAC disease, recombinant antigens may be useful as indicators of disease.

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.

Antimycobacterial antibody levels in pleural fluid as reflection of passive diffusion from serum

The objective of this study was the prospective evaluation of the relationship between serum and pleural fluid antibody levels to mycobacterial antigens and their role in the diagnosis of tuberculous pleuritis. The setting was a tertiary care medical center. Thirteen patients with tuberculous pleuritis and 53 control subjects with pleural effusion (22 with carcinoma, 17 with cardiac failure, and 14 with empyema or parapneumonic effusion) were studied. The level of IgG was measured by ELISA. The median titers of antibody to both Mycobacterium tuberculosis and M avium were significantly higher in the serum and pleural fluid of the patients with tuberculosis than in the control patients. There was a very close relationship between the levels of M tuberculosis (r = 0.95) and M avium (r = 0.94) antibodies in the serum and pleural fluid. We concluded that the levels of antimycobacterial IgG in pleural fluid, adjusted to constant protein concentration, are very closely related to the serum levels. Therefore, these antibodies in the pleural fluid probably result from passive diffusion from serum and not local production. Measurement of pleural fluid antibody levels will not add diagnostic sensitivity or specificity to that achieved with serodiagnosis.

Implications of antibodies to pyruvylated glucose in healthy populations for mycobacterioses and other infectious diseases

Members of the Mycobacterium avium-Mycobacterium intracellulare (MAI) complex are typeable because each serovar is characterized by its own specific antigenic glycolipid. By means of an enzyme-linked immunosorbent assay, we studied serum specimens obtained from 148 healthy college students for antibodies to these glycopeptidolipids. Ninety-two (61.5%) of the serum specimens were positive to the specific glycolipid antigen from MAI serovar 8. In a study of a pediatric population, antibodies appeared to develop during adolescence. Individuals with overt mycobacterial disease had a significantly lower incidence (tuberculosis patients, 34.5%; leprosy patients, 25%). We found a lower incidence of positive results in a survey of 96 Japanese serum specimens (29.1%), but the results from a survey of sera obtained from Bombay, India, indicated a large degree of reactivity (55.5%). Antibodies to other MAI serovars (serovars 2, 4, and 11) were not found, except antibodies to MAI serovar 21 were seen in the same individuals with antibodies to serovar 8. The dominant epitope of the MAI serovar 8-specific glycopeptidolipid is a terminal pyruvylated 3-O-methylglucose residue [4,6-(1'-carboxyethylidene)-3-O-methyl-alpha-D-glucopyranosyl] unit, whereas that of the MAI serovar 21 has the same terminal pyruvylated glucose devoid of the 3-methoxy group. Thus the antibodies appear specific for the pyruvylated glucose. It is unclear whether the high prevalence of antibodies to these epitopes reflects a high incidence of subclinical colonization or infection with certain MAI serovars or whether they are acquired through contact with some other related antigen source.