A role for IL-12 receptor expression and signal transduction in host defense in leprosy.

The generation of cell-mediated immunity against intracellular infection involves the production of IL-12, a critical cytokine required for the development of Th1 responses. The biologic activities of IL-12 are mediated through a specific, high affinity IL-12R composed of an IL-12Rbeta1/IL-12Rbeta2 heterodimer, with the IL-12Rbeta2 chain involved in signaling via Stat4. We investigated IL-12R expression and function in human infectious disease, using the clinical/immunologic spectrum of leprosy as a model. T cells from tuberculoid patients, the resistant form of leprosy, are responsive to IL-12; however, T cells from lepromatous patients, the susceptible form of leprosy, do not respond to IL-12. We found that the IL-12Rbeta2 was more highly expressed in tuberculoid lesions compared with lepromatous lesions. In contrast, IL-12Rbeta1 expression was similar in both tuberculoid and lepromatous lesions. The expression of IL-12Rbeta2 on T cells was up-regulated by Mycobacterium leprae in tuberculoid but not in lepromatous patients. Furthermore, IL-12 induced Stat4 phosphorylation and DNA binding in M. leprae-activated T cells from tuberculoid but not from lepromatous patients. Interestingly, IL-12Rbeta2 in lepromatous patients could be up-regulated by stimulation with M. tuberculosis. These data suggest that Th response to M. leprae determines IL-12Rbeta2 expression and function in host defense in leprosy.

T-cell release of granulysin contributes to host defense in leprosy.

A novel mechanism by which T cells contribute to host defense against microbial pathogens is release of the antimicrobial protein granulysin. We investigated the role of granulysin in human infectious disease using leprosy as a model. Granulysin-expressing T cells were detected in cutaneous leprosy lesions at a six-fold greater frequency in patients with the localized tuberculoid as compared with the disseminated lepromatous form of the disease. In contrast, perforin, a cytolytic molecule that colocalizes with granulysin in cytotoxic granules, was expressed at similar levels across the spectrum of disease. Within leprosy lesions, granulysin colocalized in CD4+ T cells and was expressed in CD4+ T-cell lines derived from skin lesions. These CD4+ T-cell lines lysed targets by the granule exocytosis pathway and reduced the viability of mycobacteria in infected targets. Given the broad antimicrobial spectrum of granulysin, these data provide evidence that T-cell release of granulysin contributes to host defense in human infectious disease.

Decreases in mean hemoglobin and serum albumin values in erythema nodosum leprosum and lepromatous leprosy.

Changes in hemoglobin (HGB) and serum albumin (SA) concentration associated with the onset of symptomatic erythema nodosum leprosum (ENL) were studied by comparing the values obtained on the day thalidomide or prednisone therapy commenced, with each patients' preceding values. In three groups of ENL patients mean HGB values fell with statistical significance: 1) in 38 patients who had been begun on thalidomide in the decade of the 1990s and who had been receiving dapsone for a minimum of 6 months, mean HGB values fell from 13.19 gm/dl to 12.27 gm/dl, or 7.0%, p = 6.0 x 10(-6); 2) in 8 patients who were in the active patient file not overlapping with the preceding group, and who had been on dapsone for a minimum of 6 months, mean HGB values feel from 13.40 gm/dl to 11.96 gm/dl, or 10.7%, p = 0.0015; and 3) in 8 patients not overlapping with the preceding groups, who were treated with rifampin and minocylcine or clarithromycin mean HGB values fell from 13.25 gm/dl to 12.48 gm/dl, or 5.8%, p = 0.0035. In two groups of ENL patients SA values also fell with statistical significance: 1) in 34 patients who were begun on thalidomide in the decade of the 1990s and who had been on dapsone for a minimum of 6 months, mean SA values fell from 4.14 gm/dl to 3.77 gm/dl, or 8.9%, p = 1.2 x 10(-5); and 2) in 10 patients from the active file not overlapping with the preceding group, and who had been on dapsone for a minimum of 6 months, mean SA values fell from 4.45 gm/dl to 4.06 gm/dl, or 8.8%, p = 0.039. A brisk fall in HGB values was often accompanied by a fall in SA concentration, and vice versa. Recovery from extreme falls in HGB and SA values was complete in 13 weeks. Recovery occurred in the presence of continued dapsone treatment. The falls could be rapid, occurring too soon to be the result of decreased erythropoiesis or hepatic SA synthesis. This study provides no direct evidence as to the mechanism responsible for the fall in these two parameters, but an interleukin-6 mediated hemodilution is an attractive hypothesis. The ENL-associated fall in HGB values was distinct from dapsone-induced hemolysis and the anemia of chronic disease. The ENL-associated anemia is not a good reason to discontinue dapsone therapy.

Trials of daily, long-term minocycline and rifampin or clarithromycin and rifampin in the treatment of borderline lepromatous and lepromatous leprosy.

Daily, long-term treatment with minocycline 100 mg and rifampin 600 mg was initiated in 24 previously untreated borderline lepromatous (BL) and lepromatous (LL) patients for a total of 646 patient-months, averaging 26.9 months per patient. The same regimen was started in 12 BL and LL patients having a bacteriologic relapse for a total of 379 patient-months, averaging 32.5 months per patient, and in 12 patients judged to be at high risk for relapse for a total of 354 patient-months, averaging 29.5 months per patient. Daily, long-term treatment with clarithromycin 500 mg and rifampin 600 mg was initiated in 8 previously untreated BL and LL patients for a total of 174 patient-months, averaging 21.8 months per patient. The results in these 56 patients were compared to those obtained in 34 previously untreated BL and LL patients who were treated concurrently receiving daily, long-term dapsone 100 mg and rifampin 600 mg. No evidence of dangerous drug reactions or bone marrow, kidney or liver toxicity was seen in any of these five patient groups. Drug intolerance in 10 of the 90 patients studied necessitated discontinuing the chosen regimen, 4 from rifampin, 3 from dapsone, 2 from minocycline and 1 of undetermined attribution. The use of either minocycline or clarithromycin in conjunction with rifampin appears to pose no great risk when used long term.

A role for CD40-CD40 ligand interactions in the generation of type 1 cytokine responses in human leprosy.

The interaction of CD40 ligand (CD40L) expressed by activated T cells with CD40 on macrophages has been shown to be a potent stimulus for the production of IL-12, an obligate signal for generation of Th1 cytokine responses. The expression and interaction of CD40 and CD40L were investigated in human infectious disease using leprosy as a model. CD40 and CD40L mRNA and surface protein expression were predominant in skin lesions of resistant tuberculoid patients compared with the highly susceptible lepromatous group. IL-12 release from PBMC of tuberculoid patients stimulated with Mycobacterium leprae was partially inhibited by mAbs to CD40 or CD40L, correlating with Ag-induced up-regulation of CD40L on T cells. Cognate recognition of M. leprae Ag by a T cell clone derived from a tuberculoid lesion in the context of monocyte APC resulted in CD40L-CD40-dependent production of IL-12. In contrast, M. leprae-induced IL-12 production by PBMC from lepromatous patients was not dependent on CD40L-CD40 ligation, nor was CD40L up-regulated by M. leprae. Furthermore, IL-10, a cytokine predominant in lepromatous lesions, blocked the IFN-gamma up-regulation of CD40 on monocytes. These data suggest that T cell activation in situ by M. leprae in tuberculoid leprosy leads to local up-regulation of CD40L, which stimulates CD40-dependent induction of IL-12 in monocytes. The CD40-CD40L interaction, which is not evident in lepromatous leprosy, probably participates in the cell-mediated immune response to microbial pathogens.

Evidence for human CD4+ T cells in the CD1-restricted repertoire: derivation of mycobacteria-reactive T cells from leprosy lesions.

Both the CD4-CD8- (double negative) and CD4-CD8+ T cell lineages have been shown to contain T cells which recognize microbial lipid and glycolipid Ags in the context of human CD1 molecules. To determine whether T cells expressing the CD4 coreceptor could recognize Ag in the context of CD1, we derived CD4+ T cell lines from the lesions of leprosy patients. We identified three CD4+ Mycobacterium leprae-reactive, CD1-restricted T cell lines: two CD1b restricted and one CD1c restricted. These T cell lines recognize mycobacterial Ags, one of which has not been previously described for CD1-restricted T cells. The response of CD4+ CD1-restricted T cells, unlike MHC class II-restricted T cells, was not inhibited by anti-CD4 mAb, suggesting that the CD4 coreceptor does not impact positive or negative selection of CD1-restricted T cells. The CD4+ CD1-restricted T cell lines produced IFN-gamma and GM-CSF, the Th1 pattern of cytokines required for cell-mediated immunity against intracellular pathogens, but no detectable IL-4. The existence of CD4+ CD1-restricted T cells that produce a Th1 cytokine pattern suggests a contributory role in immunity to mycobacterial infection.

Frequency and extent of thickening of the nucleated epidermis in leprosy lesions.

Using 28 specimens of clinically normal skin from lepromatous leprosy subjects as a standard for comparison, the mean thickness of the nucleated epidermis was found to be significantly increased in untreated lesions from 16 borderline tuberculoid, 21 erythema nodosum leprosum (ENL), and 14 reversal reaction patients, but was unchanged in borderline lepromatous and lepromatous patients. Using specimens from 36 untreated lepromatous and borderline lepromatous lesions as the standard for comparison with the lesions of reversal reactions or ENL which these patients eventually developed, there was a significant thickening of the nucleated epidermis in both reactional states. In both comparison groups, there was a greater mean increase and a larger frequency of thickening in the ENL lesions than in those with reversal reactions. In the borderline tuberculoid and reversal reaction lesions the increase can be understood as secondary to the presence of gamma interferon or interleukin-2. The increase in thickness in the ENL lesions is more difficult to explain, but it is not inconsistent with a role for these same two cytokines.

IL-18 promotes type 1 cytokine production from NK cells and T cells in human intracellular infection.

We investigated the role of IL-18 in leprosy, a disease characterized by polar cytokine responses that correlate with clinical disease. In vivo, IL-18 mRNA expression was higher in lesions from resistant tuberculoid as compared with susceptible lepromatous patients, and, in vitro, monocytes produced IL-18 in response to Mycobacterium leprae. rIL-18 augmented M. leprae-induced IFN-gamma in tuberculoid patients, but not lepromatous patients, while IL-4 production was not induced by IL-18. Anti-IL-12 partially inhibited M. leprae-induced release of IFN-gamma in the presence of IL-18, suggesting a combined effect of IL-12 and IL-18 in promoting M. leprae-specific type 1 responses. IL-18 enhanced M. leprae-induced IFN-gamma production rapidly (24 h) by NK cells and in a more sustained manner (5 days) by T cells. Finally, IL-18 directly induced IFN-gamma production from mycobacteria-reactive T cell clones. These results suggest that IL-18 induces type 1 cytokine responses in the host defense against intracellular infection.

CD1 expression by dendritic cells in human leprosy lesions: correlation with effective host immunity.

A potential role for the CD1 family of lipid Ag-presenting molecules in antimicrobial immunity in vivo was investigated in human leprosy skin lesions. Strong induction of three CD1 proteins (CD1a, -b, and -c) was observed in dermal granulomas in biopsy samples of involved skin from patients with the tuberculoid form of leprosy or with reversal reactions, which represent clinical patterns of disease associated with active cellular immunity to Mycobacterium leprae. In contrast, lesions from patients with the lepromatous form of the disease who lack effective cell-mediated immunity to the pathogen did not show induction of CD1 proteins. Thus, expression of CD1 correlated directly with effective immunity to M. leprae, as assessed by the clinical course of infection. CD1a, -b, and -c could be induced to similar levels on monocytes from the blood of either tuberculoid or lepromatous leprosy patients. This suggested that the absence of expression in lepromatous lesions was most likely due to local factors at the site of infection as opposed to a primary defect of the CD1 system itself. The majority of cells expressing CD1 in leprosy lesions were identified as a population of CD83+ dendritic cells. Initial in vitro studies of the Ag-presenting function of CD1+CD83+ monocyte-derived dendritic cells showed that such cells were highly efficient APCs for CD1-restricted T cells. These results indicate that the CD1 system can be up-regulated in human infectious diseases in vivo, and may play a role in augmenting host defense against microbial pathogens.

B7-1, but not CD28, is crucial for the maintenance of the CD4+ T cell responses in human leprosy.

We used human leprosy as a model to compare patterns of costimulatory molecule expression in respect to the clinical/immunologic spectrum of disease. We found that B7-1, B7-2, and CD28 transcripts dominated in tuberculoid leprosy patients, who have potent T cell responses to Mycobacterium leprae. In contrast, CTLA-4 was more strongly expressed in lesions from lepromatous patients, who manifest specific T cell anergy to the leprosy bacterium. T cell clones from tuberculoid lesions were CD4+CD28+ or CD4+CD28-, and T cell clones from lepromatous lesions were predominantly CD8+CD28-. The M. leprae-specific recall response of CD4+ T cell clones from tuberculoid lesions was blocked by anti-B7-1 mAb, but not by anti-B7-2 mAb or CTLA-Ig. However, anti-CD28 and anti-CTLA-4 mAbs did not block activation of clones from tuberculoid lesions, suggesting that B7-1 may utilize another costimulatory pathway. Peripheral blood T cell responses in the lepromatous form were strongly regulated by CD28 during T cell activation, in contrast to the tuberculoid form. Thus, B7-1 costimulation could play a role in maintaining a strong immune response to the pathogen.

Delayed-type hypersensitivity reactions followed by erythema nodosum leprosum.

Reported herein are 13 borderline lepromatous (BL) or subpolar lepromatous (LLs) patients who presented with or developed delayed-type hypersensitivity (DTH) reactions after initiation of antibacterial therapy, but who subsequently developed erythema nodosum leprosum (ENL), the DTH to ENL group. During the same time, three LLs patients had ENL followed by relapse-associated DTH, a significant (p < 0.05) difference in sequence of the two conditions. The DTH to ENL group had statistically significant higher biopsy indexes at the time of diagnosis of the DTH reaction compared with two DTH control groups, 7 multibacillary patients presenting with DTH reactions and 15 BL or LLs who developed DTH reactions after starting treatment but had no ENL. DTH-associated histologic changes were less well developed in the DTH to ENL group than in either of the two control groups. In the DTH to ENL group, 77% required prednisone in addition to thalidomide to achieve a complete remission in contrast to only 10% of 21 ENL clinical controls. In the DTH to ENL group, the classical histologic ENL pattern was present in only 31% of these patients, in contrast to 88% of 33 ENL histologic controls. In 9 of 9 of the DTH to ENL patients studied, after the ENL remitted, Mycobacterium leprae-sonicate-stimulated lymphocyte transformation tests gave stimulation indexes within the range of our tuberculoid (TT) and borderline tuberculoid (BT) patients, in contrast to absent responses in 6 ordinary, longterm-treated patients who had had ENL.

Determinants of T cell reactivity to the Mycobacterium leprae GroES homologue.

The 10-kDa protein Ag of Mycobacterium leprae, a human GroES hsp10 cognate, is a major T cell Ag in human leprosy infection. We investigated the mechanism for T cell responsiveness to this Ag according to the trimolecular interaction between T cell, peptide, and Ag-presenting element. This research was accomplished by mapping T cell epitopes in leprosy patients and correlating these responses with peptide-MHC binding affinities. We found that the majority of tuberculoid leprosy patients responded to peptides corresponding to residues 25-39 and 28-42. Truncation analysis of these peptides mapped the exact epitope to be within the overlapping region comprising residues 28-39. Responsiveness was correlated with the HLA-DRB5*0101 allele, which bound the peptides with moderate affinity. This allele is linked to HLA-DR2, which is associated with the resistant form of leprosy. Therefore, T cell responsiveness in tuberculoid leprosy may be mediated by the ability of HLA-DRB5*0101 to bind and present peptides of the immunodominant 10-kDa Ag.

Interferon-gamma differentially regulates interleukin-12 and interleukin-10 production in leprosy.

The ability of monocytes to influence the nature of the T cell response to microbial pathogens is mediated in part by the release of cytokines. Of particular importance is the release of IL-12 and IL-10 by cells of the monocyte/macrophage lineage upon encountering the infectious agent. IL-12 promotes cell mediated immunity (CMI) to intracellular pathogens by augmenting T-helper type 1 responses, whereas IL-10 downregulates these responses. The ability of IFN-gamma to modulate the balance between IL-12 and IL-10 production was examined by studying leprosy as a model. In response to Mycobacterium leprae stimulation, IFN-gamma differentially regulated IL-12 and IL-10 production resulting in upregulation of IL-12 release and downregulation of IL-10 release. Furthermore, we determined that the mechanism by which IFN-gamma downregulates IL-10 was through the induction of IL-12. The data suggest a model of lymphocyte-monocyte interaction whereby the relative presence or absence of IFN-gamma in the local microenvironment is a key determinant of the type of monocyte cytokine response, and hence the degree of CMI in the host response to infection.

IL-15, an immunomodulator of T cell responses in intracellular infection.

IL-15 is a novel cytokine with potent T cell growth factor activity. Here, we investigated the role of IL-15 in the human immune response to intracellular infection by studying patients leprosy. We found that IL-15 mRNA and protein were more strongly expressed in immunologically resistant tuberculoid patients than in with unresponsive and susceptible lepromatous patients. In vitro, Mycobacterium leprae induced IL-15 secretion from peripheral blood monocytes. Furthermore, rIL-15 by itself and in combination with rIL-2 or rIL-7 augmented PBMC proliferative responses to the pathogen. Although rIL-15 expanded the CD3-CD56+ (NK) subset, rIL-15 combined with M. leprae induced the expansion of CD3+CD56+ T cells. Immunohistologic analysis of leprosy skin lesions indicated that the frequency of CD56+ cells was greatest in the group of patients with high IL-15 expression, and that >90% of the CD56+ cells in lesions were CD3+ T cells. Therefore, IL-15 augments the local T cell response to human intracellular pathogen.

IL-7 in the cell-mediated immune response to a human pathogen.

The goal of the present study was to investigate the role of IL-7 in regulating immune responses to infection. Leprosy provides a model for understanding human immune responses to infection; the disease presents as a spectrum in which the clinical manifestations correlate with the levels of cell-mediated immunity to the pathogen, Mycobacterium leprae. To determine whether IL-7 is produced at the site of infection in leprosy, we used the PCR to measure IL-7 and IL-7R mRNA in skin lesions. IL-7 mRNA was more strongly expressed in the tuberculoid form of the disease, in which the infection is limited (mean cpm = 48 +/- 8; n = 11), as compared with the progressive lepromatous form (17 +/- 2; n = 11). IL-7R mRNA, both membrane-bound and soluble forms, were also more strongly expressed in tuberculoid lesions, although these differences were not as striking as those for IL-7. The cellular source of IL-7 included Ag-stimulated monocytes and IFN-gamma-induced keratinocytes. M. leprae-induced PBMC responses in tuberculoid patients involved up-regulation of IL-7 and IL-7R mRNA and was IL-7 dependent. In contrast, M. leprae did not induce IL-7 mRNA in lepromatous patients, and their T cell responses were weakly augmented by rIL-7. These data suggest that IL-7, produced at the site of disease, contributes to the cell-mediated immune response to human pathogens.

Overexpression of IL-10 in atopic dermatitis. Contrasting cytokine patterns with delayed-type hypersensitivity reactions.

The skin lesions of patients with atopic dermatitis provide a model to study immunoregulation in human allergy. To determine the local cytokine pattern of cells present (both endogenous and recruited) at the site of disease, we extracted RNA from skin biopsy specimens from patients with atopic dermatitis, allergic contract dermatitis, and positive tuberculin reactions and used PCR to assay for cytokine mRNA. cDNAs were normalized to the intensity of the CD3 delta PCR product as a marker of T cell mRNA. We found overexpression of IL-10 mRNA in atopic dermatitis lesions, in comparison with allergic contact dermatitis lesions and tuberculin reactions. In contrast, IL-4 mRNA was most strongly expressed in allergic contact dermatitis lesions and IFN-gamma mRNA was the predominant cytokine in tuberculin reactions. Using an anti-IL-10 mAb with immunoperoxidase, we localized IL-10 protein to large mononuclear cells in the dermal infiltrate of atopic lesions. After immunomagnetic sorting of mononuclear cell populations from PBMC of atopic dermatitis subjects, IL-10 mRNA as measured by PCR was found to be strongly expressed in CD14+ cells. Spontaneous release of IL-10 from PBMC-derived adherent cells was greater in atopic dermatitis donors than normal controls. We therefore renormalized skin biopsy cDNA according to the level of beta-actin PCR product, as a marker of total cellular mRNA, and found by PCR that IL-10 was nevertheless greatest in atopic dermatitis subjects. We conclude that the relative overexpression of IL-10 in atopic dermatitis greatest in atopic dermatitis subjects. We conclude that the relative overexpression of IL-10 in atopic dermatitis may contribute to the up-regulation of humoral responses and the down-regulation of Th1 responses.