Specificity and function of immunogenic peptides from the 35-kilodalton protein of Mycobacterium leprae.
We identified a T-cell determinant of the 35-kDa antigen of Mycobacterium leprae which is discriminatory against cross-sensitization by its closely related homologue in Mycobacterium avium. From synthetic peptides covering the entire sequence, those with the highest affinity and permissive binding to purified HLA-DR molecules were evaluated for the stimulation of proliferation of peripheral blood mononuclear cells (PBMCs) from leprosy patients and healthy sensitized controls. Responses to the peptide pair 206-224, differing by four residues between M. leprae and M. avium, involved both species-specific and cross-reactive T cells. Lymph node cell proliferation in HLA-DRB1*01 transgenic mice was reciprocally species specific, but only the response to the M. leprae peptide in the context of DR1 was immunodominant. Of the cytokines in human PBMC cultures, gamma interferon production was negligible, while interleukin 10 (IL-10) responses in both patients and controls were more pronounced. IL-10 was most frequently induced by the shared 241-255 peptide, indicating that environmental cross-sensitization may skew the response toward a potentially pathogenic cytokine phenotype. (+info)
Reduced pyrazinamidase activity and the natural resistance of Mycobacterium kansasii to the antituberculosis drug pyrazinamide.
Pyrazinamide (PZA), an analog of nicotinamide, is a prodrug that requires conversion to the bactericidal compound pyrazinoic acid (POA) by the bacterial pyrazinamidase (PZase) activity of nicotinamidase to show activity against Mycobacterium tuberculosis. Mutations leading to a loss of PZase activity cause PZA resistance in M. tuberculosis. M. kansasii is naturally resistant to PZA and has reduced PZase activity along with an apparently detectable nicotinamidase activity. The role of the reduction in PZase activity in the natural PZA resistance of M. kansasii is unknown. The MICs of PZA and POA for M. kansasii were determined to be 500 and 125 micrograms/ml, respectively. Using [14C]PZA and [14C]nicotinamide, we found that M. kansasii had about 5-fold-less PZase activity and about 25-fold-less nicotinamidase activity than M. tuberculosis. The M. kansasii pncA gene was cloned on a 1.8-kb BamHI DNA fragment, using M. avium pncA probe. Sequence analysis showed that the M. kansasii pncA gene encoded a protein with homology to its counterparts from M. tuberculosis (69.9%), M. avium (65.6%), and Escherichia coli (28.5%). Transformation of naturally PZA-resistant M. bovis BCG with M. kansasii pncA conferred partial PZA susceptibility. Transformation of M. kansasii with M. avium pncA caused functional expression of PZase and high-level susceptibility to PZA, indicating that the natural PZA resistance in M. kansasii results from a reduced PZase activity. Like M. tuberculosis, M. kansasii accumulated POA in the cells at an acidic pH; however, due to its highly active POA efflux pump, the naturally PZA-resistant species M. smegmatis did not. These findings suggest the existence of a weak POA efflux mechanism in M. kansasii. (+info)
The p47(phox-/-) mouse model of chronic granulomatous disease has normal granuloma formation and cytokine responses to Mycobacterium avium and Schistosoma mansoni eggs.
Chronic granulomatous disease (CGD) is a genetic disorder of NADPH oxidase in which phagocytes are defective in generating reactive oxidants. CGD patients suffer from recurrent infections and exuberant and persistent tissue granuloma formation. We hypothesized that abnormal granulomata in CGD may result from aberrant T-cell-mediated cytokine responses. To assess Th-1-type cytokine responses and granulomata, we challenged p47(phox-/-) and wild-type mice with avirulent (SmD) or virulent (SmT) variants of Mycobacterium avium 2-151. To assess Th-2-type cytokine responses and granulomata, we used Schistosoma mansoni eggs (SME). Mononuclear cells were harvested, and cytokine responses were determined by enzyme-linked immunosorbent assay or reverse transcriptase PCR. Following SmD or SmT challenge, splenocytes from p47(phox-/-) and wild-type mice generated similar polar Th-1 responses (increased levels of gamma interferon and basal levels of interleukin 4 [IL-4] and IL-5). By 8 weeks after SmT challenge, exuberant splenic granulomata developed in p47(phox-/-) and wild-type mice. After SME challenge, thoracic lymph node mononuclear cells from p47(phox-/-) and wild-type mice generated similar mixed Th-1 and Th-2 cytokine responses to SME antigen and concanavalin A. Peak lung granuloma sizes and rates of regression were similar in p47(phox-/-) and wild-type mice. These results suggest that exuberant granulomatous inflammation in CGD is probably not the result of skewing of T-cell responses toward the Th-1 or Th-2 pole. Appropriate regression of established tissue granulomata in p47(phox-/-) mice challenged with SME suggests that abnormal granuloma formation in CGD is stimulus dependent and is not an invariant feature of the disease. (+info)
Differential avian and human tuberculin skin testing in non-tuberculous mycobacterial infection.
OBJECTIVE: To determine the sensitivity of differential avian and human delayed-type hypersensitivity skin testing in the diagnosis of non-tuberculous mycobacterial lymphadenitis. METHOD: Retrospective review of all patients with culture proved non-tuberculous mycobacterial lymph node infections who also had differential avian and human skin testing performed over a 10 year period from 1986 to 1996. RESULTS: One hundred and twenty four patients had non-tuberculous mycobacteria isolated from lymph nodes over this period, 59 of whom had differential skin testing performed. The sensitivity of a response of >/= 10 mm to the avian precipitin was 58 of 59. No patient had both a negative human and avian Mantoux. The sensitivity of the human Mantoux alone for diagnosing non-tuberculous mycobacterial infection was 81% for a response of >/= 5 mm and 66% for >/= 10 mm. Ten patients had a 0 human response. Fifty five of the 59 patients had an avian response at least 2 mm greater than the human response. CONCLUSION: The avian Mantoux is a very sensitive method of diagnosing non-tuberculous mycobacterial infection in children. The human Mantoux is not sensitive enough to be used alone as a surrogate to diagnose non-tuberculous mycobacterial infection. (+info)
Inflammatory pseudotumor in a cat with cutaneous mycobacteriosis.
A 5-year-old, castrated male, domestic Shorthair Cat had an ulcerated mass with fistulous tracts on the left hind paw. Homogeneous tan tissue diffusely infiltrated the dermis and subcutis of the paw and extended proximally so that, short of amputation, complete excision was not feasible. Biopsy specimens consisted of granulation tissue with marked proliferation of spindle cells. Neutrophils and histiocytic cells were scattered among the spindle cells. The histiocytic cells had abundant foamy or vacuolated cytoplasm, but features of granulomatous inflammation, such as epithelioid macrophages or granuloma formation, were not observed. The initial impression was inflammatory granulation tissue, but the degree of fibroplasia prompted inclusion of fibrosarcoma in the differential diagnosis. Cutaneous mycobacteriosis was diagnosed when numerous acid-fast bacteria were identified with Kinyoun's stain; Mycobacterium avium was subsequently cultured. The cat was euthanatized because of lack of response to enrofloxacin therapy. At necropsy, lesions were localized to the hind limb. Not only is mycobacteriosis an uncommon cause of cutaneous masses in cats, but this case was unusual because of the lack of granuloma formation and the similarity of the mass to a spindle cell tumor. (+info)
Prevalence of Mycobacterium avium in slaughter pigs in The Netherlands and comparison of IS1245 restriction fragment length polymorphism patterns of porcine and human isolates.
A significant increase in the incidence of caseous lesions in the lymph nodes of slaughter pigs prompted a large-scale investigation in five slaughterhouses in The Netherlands. In total, 158,763 pigs from 2,899 groups underwent gross examination. At least one pig with caseous lesions in the submaxillary and/or mesenteric lymph nodes was observed in each of 154 of the 2,899 groups examined (5%). In total, 856 pigs (0.5%) were affected. As many as five pigs in each of 141 of the 154 positive groups (91.5%) had lymph node lesions. Greater numbers of pigs with affected lymph nodes were found in 13 groups (8.5%). Four pigs had lesions in the kidneys, liver, or spleen. Acid-fast bacteria were detected by microscopic examination of 121 of 292 Ziehl-Neelsen-stained smears of caseous lesions (41%). In a follow-up study, Mycobacterium avium complex (MAC) bacteria were isolated from 219 of 402 affected lymph nodes (54.2%). Ninety-one of the isolated strains were analyzed by restriction fragment length polymorphism (RFLP) typing with insertion sequence IS1245 as a probe. All but 1 of these 91 strains contained IS1245 DNA, indicating that pigs in The Netherlands carried almost exclusively M. avium bacteria and no other bacteria of MAC. Only one pig isolate exhibited the bird-type RFLP pattern. MAC isolates from 191 human patients in The Netherlands in 1996 were also typed by RFLP analysis. Computer-assisted analysis showed that the RFLP patterns of 61% of the human isolates and 59% of the porcine isolates were at least 75% similar to the RFLP patterns of the other group of strains. This indicates that pigs may be an important vehicle for M. avium infections in humans or that pigs and humans share common sources of infection. (+info)
Apoptosis of Mycobacterium avium-infected macrophages is mediated by both tumour necrosis factor (TNF) and Fas, and involves the activation of caspases.
Mycobacterium avium causes disseminated infection in AIDS patients and several forms of infection in immunocompetent hosts. Recent studies have shown that M. avium infection of macrophages in vitro leads to apoptosis of significant numbers of infected cells. Several strains of M. avium used to infect human macrophages for 5 days (multiplicity of infection of 10) triggered 28-46% higher levels of apoptosis than observed with uninfected macrophages at the same time points. Mycobacterium avium strains unable to replicate intracellularly (rep-) resulted in a 15% rate of apoptosis, while M. smegmatis-infected monolayers showed the same percentage of apoptotic cells as the uninfected macrophage control. The presence of anti-TNF-alpha antibody reduced apoptosis to 17% and the presence of anti-Fas antibody reduced apoptosis to 10%. When both antibodies were used together, the apoptosis level was 5% above the control. Treatment with TGF-beta also reduced the number of apoptotic cells in infected monolayers. If intracellular growth was inhibited, apoptosis of macrophages decreased significantly. It was also shown that apoptosis was associated with IL-1 beta-converting enzyme (ICE) activation and was significantly reduced by a caspase inhibitor. Gaining understanding of the mechanisms of M. avium-associated apoptosis of macrophages will provide important insight into M. avium pathogenesis. (+info)
A role for CD45RBlow CD38+ T cells and costimulatory pathways of T-cell activation in protection of non-obese diabetic (NOD) mice from diabetes.
Non-obese diabetic (NOD) mice spontaneously develop autoimmune insulin-dependent diabetes mellitus (IDDM). Infection of the animals with mycobacteria, or immunization with mycobacteria-containing adjuvant, results in permanent protection of NOD mice from diabetes and we have recently reported that the phenomenon is associated with increased numbers of interferon-gamma-producing T cells, possessing increased cytotoxic activity, and also with augmented numbers of activated immunoglobulin M-positive (IgM+) B cells. Here, we have investigated whether protection of NOD mice from IDDM was associated with changes on costimulatory pathways of T and B cells, namely CD28/CTLA-4-B7 and CD40-CD40 ligand (CD40L) and we also further characterized protective T helper (Th) cells with regards to the expression of the differentiation markers CD45RB and CD38. We report that Th cells involved in diabetes vaccination of NOD mice by mycobacterial infection seem to belong to CD45RBlo CD38+ phenotype. The protective effect of Mycobacterium avium infection is also associated with increased CD40L and CTLA-4- expressing Th cells and with the generation of a CD40- IgG+ B cells. Our data are consistent with induction by mycobacterial infection of regulatory CD45RBlo CD38+ Th cells with the ability to trigger deletion or anergy of peripheral self-reactive lymphocytes, with shutting down of IgG+ B-cell response. They also implicate a role for IgG+ B cells in the autoimmune aggression of the endocrine pancreas of NOD mice. (+info)