Suppressor T lymphocytes from lepromatous leprosy skin lesions

The immune response in leprosy forms a spectrum with lepromatous leprosy patients exhibiting specific unresponsiveness to antigens of Mycobacterium leprae. This unresponsiveness is thought to be related to the prevalence of T8-positive lymphocyte in these lepromatous lesions. To analyze the immunoregulatory function of these T8 cells, we developed simple procedures to extract lymphocytes from skin biopsy specimens of patients with leprosy. These lymphocytes were sorted for T8 and T4 positive cells, and cell lines were established by expansion with interleukin 2 (IL 2) and irradiated feeder cells. All T8 positive lines tested were positive for IL 2 receptors and HLA-DR determinants. These lines were additionally assayed for lepromin-induced suppression of the normal peripheral blood lymphocyte Con A proliferative response. Thirteen of 32 lines from six lepromatous patients showed significant suppressor activity, whereas nine lines from six tuberculoid patients and one line from normal peripheral blood failed to show suppression (p less than 0.001). Taken together, the finding of M. leprae-triggered suppressor cells within lepromatous skin lesions may in part explain the M. leprae unresponsiveness of lepromatous leprosy patients.     

M. leprae and PPD-triggered T cell lines in tuberculoid and lepromatous leprosy

Proliferative responses of peripheral blood mononuclear cells (PBMC) to Mycobacterium leprae and bacillus Calmette Guerin-derived purified protein derivative (PPD) were studied in the presence or absence of interleukin 2 (IL 2) in high M. leprae responders (tuberculoid leprosy patients and healthy subjects) and low M. leprae responders (lepromatous leprosy patients). High responders in most cases developed a strong proliferative response to both antigens in the absence of IL 2. Additional IL 2 and restimulation with antigen plus autologous antigen-presenting cells (APC) allowed the derivation of antigen-specific T cell lines. The lines were assayed for proliferative responses to several mycobacterial antigens. Both PPD and M. leprae-triggered T cell lines exhibited a good proliferative response to either antigen and showed in addition a broad cross-reactivity with other mycobacteria, suggesting a preferential T cell response to epitopes shared by several mycobacterial species. Within the lepromatous group, 50% of the patients studied could mount a proliferative response to PPD antigen in the absence of IL 2, but none of them was able to do so with M. leprae antigen. The addition of IL 2 increased the number of positive responders to PPD in this group, and in some patients IL 2 was able to restore M. leprae reactivity as well, suggesting that IL 2 had overcome a suppressor mechanism. PPD and M. leprae-triggered T cell lines were obtained from these subjects (with IL 2 added from the beginning of the culture when required). M. leprae lines exhibited variable and unstable pattern of specificity, most lines exhibiting, at least transiently, a cross-reactive response to other mycobacteria, but some displaying only M. leprae-specific response. In contrast, PPD lines from these subjects consistently exhibited a good response to PPD, a lesser response to various other mycobacteria and no response to M. leprae, a pattern differing from that obtained with PPD lines of high M. leprae responders. Co-cultures of irradiated lepromatous PPD triggered T cell lines with fresh autologous PBMC non-specifically reduced the proliferative response of the latter to PPD, as well as to unrelated antigens. A similar suppression was also observed when PPD lines from one of the tuberculoid patients were assayed. PPD and M. leprae T cell lines from both high and low responders initially exhibited the same CD4+ CD8- phenotype. In all cases, antigenic specificity declined and could not be maintained after 5 to 8 wk of continuous culture, a change associated with the progressive appearance of CD8+ and Leu8+ cells.     

T cell defect in lepromatous leprosy is reversible in vitro in the absence of exogenous growth factors

T lymphocytes from patients with lepromatous leprosy (LL) characteristically fail to respond to Mycobacterium leprae. This specific immunologic defect is thought to contribute to the aggressive clinical course that typifies patients with LL. We report that although fresh CD4+ (helper) T cells from most LL patients are specifically unresponsive to M. leprae, after culture in medium alone for 48 hr the same cells respond to M. leprae antigens. The recovery of T cell function is specific for M. leprae, occurs at the level of responder CD4+ T cells, and is not affected by monocytes or CD8+ (suppressor) T cells. Recovery of T cell reactivity is blocked by the presence of M. leprae bacilli in the preculture medium. These findings indicate that despite the apparent specific anergy seen in patients with LL, the T cells of most LL patients can respond to M. leprae. Their failure to do so, in vivo, may be due to the persistence of antigen, which renders antigen-reactive T cells nonresponsive either directly or via activation of CD4+ suppressor cells.     

In situ identification of cells in human leprosy granulomas with monoclonal antibodies to interleukin 2 and its receptor

Leprosy is a chronic granulomatous disease with an immunologic spectrum in which lepromatous leprosy patients have defective cell-mediated immune responses, in comparison to tuberculoid leprosy patients. Immunoregulatory aspects of this spectrum were investigated by using monoclonal antibodies to interleukin 2 (IL 2), IL 2 receptors (Tac), and T lymphocyte subpopulations with immunoperoxidase techniques on frozen sections of skin biopsy specimens from 10 tuberculoid and 10 lepromatous patients. A comparison of IL 2+ cells revealed markedly fewer IL 2+ cells in lepromatous specimens (lep. 0.028% +/- 0.02 vs tub. 0.46% +/- 0.28, p less than 0.001). These IL 2+ cells were large, exhibited cytoplasmic staining, and on double immunostaining were Leu-4+, Leu-3a+, Leu-2a-, Tac-, and OKT6-, consistent with the fact they are IL 2 producers. Equivalent numbers of Tac+ cells were observed in both lepromatous and tuberculoid granulomas (lep. 1.5% +/- 0.5 vs tub. 2.1% +/- 0.7, p, NS), suggesting that the responder cells are present in both conditions. The tuberculoid granuloma was highly organized, composed of a central core of mature macrophages, Leu-3a+ and Tac+ cells with a surrounding mantle of Leu-2a+, Leu-3a+, IL 2+, Tac+, and OKT6+ cells. In lepromatous granulomas, Leu-2a+, Leu-3a+, Tac+, and rare IL 2+ cells were randomly admixed with bacilli-laden macrophages. The defective cell-mediated immune responses in lepromatous leprosy appears to be associated with diminished IL 2 production and disorganization of the granuloma.     

Impairment of alternate pathway (CD2) of T cell activation in leprosy

Recent studies in basic immunology have been directed towards the understanding of the mechanism of T cell activation. T cells can be activated to proliferatevia the classical pathway through the antigen receptor (CD3-Ti) orvia the alternate pathway through the CD2 receptor. Since immunologic unresponsiveness in lepromatous leprosy is considered to be due to the inability of T cells to proliferate upon stimulation, we have been interested in the nature of these receptors and the activation pathways in lymphocytes of leprosy patients. In the present investigation we demonstrate: (i) CD2 receptor (E-receptor) is downregulated in bacterial index positive lepromatous leprosy patients. (ii) The alternate pathway of T cell activation is impaired in lepromatous patients as revealed by the inability of their lymphocytes to proliferate in response to a pair of mitogenic anti-CD2 monoclonals. (iii) The addition of recombinant interleukin 2in vitro restores the ability of lymphocytes from lepromatous patients to proliferate in response to anti-CD2 antibodies. (iv) Interestingly, CD2 modulation and the associated functional impairment could be brought about in peripheral blood lymphocytes from normal subjects by prior treatment withMycobacterium leprae in vitro. This approach would be useful in understanding the molecular events leading to the defective T cell functions in leprosy.     

Immunological defect in leprosy patients: altered T-lymphocyte signals

The early events of activation were studied in paucibacillary (TT/BT) and multibacillary (BL/LL) leprosy patients by stimulation of their lymphocytes with mitogenic agents (calcium ionophore A23187/PMA) and Micobacterium leprae antigen (PGL-1). Maximum proliferation in response to PMA/A23187 and PGL-1 was observed in the BT/TT patients and the control group, respectively. Inositol triphosphate (IP3) and calcium were constitutively elevated in BT/TT and LL/BL patients. PMA/A23187 caused an increase in both IP3 and [Ca2+]i in BT/TT patients and controls. PGL-1 marginally increased IP3 levels in BT/TT patients. In the LL/BL patients, although PMA/A23187 increased IP3 levels, but no change was seen in [Ca2+]i, PGL-1 had no effect. Protein kinase C levels were seen to be associated with particulate fractions in BT/TT patients and were found to increase further in response to PMA/A23187. PGL-1 did not increase translocation of protein kinase C in controls or LL/BL patients. A preactivated and sensitised state of T-lymphocytes was observed in BT/TT patients, responsive to antigen and mitogens, whereas the cells of LL/BL patients were unresponsive to PGL-1. The altered signal transduction events characterised in the MB patients thus correlate well with the anergic state of their cells.     

Field utility of phenolic glycolipid coated latex agglutination test for rapid detection of bacilliferous leprosy cases.

Serum samples were collected from eighty-three leprosy patients and twenty-five healthy controls supposedly not exposed to Mycobacterium leprae infection. Phenolic glycolipid-1 coated latex agglutination test (PGL-LAT) was carried out with the serum samples to detect antibodies specific to M. leprae. Samples showing positive agglutination were 50% in the lepromatous leprosy (LL) group showing no erythema nodosum leprosum (ENL) complications, 66.6% in LL group with ENL complication, 60% in borderline lepromatous (BL) group, 50% in borderline (BB) and 33.3% in borderline tuberculoid (BT). The patients belonging to the tuberculoid (TT) group and most of the long-term treated patients were interestingly negative, and so were sera from all the healthy controls. PGL-LAT developed by us therefore is specific and a fairly sensitive technique to detect antibodies specific to M. leprae and will be very useful in field conditions.     

Activation and cytokine profile of monocyte derived dendritic cells in leprosy: in vitro stimulation by sonicated Mycobacterium leprae induces decreased level of IL-12p70 in lepromatous leprosy

Dendritic cells (DCs) play a pivotal role in the connection of innate and adaptive immunity of hosts to mycobacterial infection. Studies on the interaction of monocyte-derived DCs (MO-DCs) using Mycobacterium leprae in leprosy patients are rare. The present study demonstrated that the differentiation of MOs to DCs was similar in all forms of leprosy compared to normal healthy individuals. In vitro stimulation of immature MO-DCs with sonicated M. leprae induced variable degrees of DC maturation as determined by the increased expression of HLA-DR, CD40, CD80 and CD86, but not CD83, in all studied groups. The production of different cytokines by the MO-DCs appeared similar in all of the studied groups under similar conditions. However, the production of interleukin (IL)-12p70 by MO-DCs from lepromatous (LL) leprosy patients after in vitro stimulation with M. leprae was lower than tuberculoid leprosy patients and healthy individuals, even after CD40 ligation with CD40 ligand-transfected cells. The present cumulative findings suggest that the MO-DCs of LL patients are generally a weak producer of IL-12p70 despite the moderate activating properties ofM. leprae. These results may explain the poor M. leprae-specific cell-mediated immunity in the LL type of leprosy.     

Human TLR1 deficiency is associated with impaired mycobacterial signaling and protection from leprosy reversal reaction

Toll-like receptors (TLRs) are important regulators of the innate immune response to pathogens, including Mycobacterium leprae, which is recognized by TLR1/2 heterodimers. We previously identified a transmembrane domain polymorphism, TLR1_T1805G, that encodes an isoleucine to serine substitution and is associated with impaired signaling. We hypothesized that this TLR1 SNP regulates the innate immune response and susceptibility to leprosy. In HEK293 cells transfected with the 1805T or 1805G variant and stimulated with extracts of M. leprae, NF-kappaB activity was impaired in cells with the 1805G polymorphism. We next stimulated PBMCs from individuals with different genotypes for this SNP and found that 1805GG individuals had significantly reduced cytokine responses to both whole irradiated M. leprae and cell wall extracts. To investigate whether TLR1 variation is associated with clinical presentations of leprosy or leprosy immune reactions, we examined 933 Nepalese leprosy patients, including 238 with reversal reaction (RR), an immune reaction characterized by a Th1 T cell cytokine response. We found that the 1805G allele was associated with protection from RR with an odds ratio (OR) of 0.51 (95% CI 0.29-0.87, p = 0.01). Individuals with 1805 genotypes GG or TG also had a reduced risk of RR in comparison to genotype TT with an OR of 0.55 (95% CI 0.31-0.97, p = 0.04). To our knowledge, this is the first association of TLR1 with a Th1-mediated immune response. Our findings suggest that TLR1 deficiency influences adaptive immunity during leprosy infection to affect clinical manifestations such as nerve damage and disability.     

Cutting edge: a Toll-like receptor 2 polymorphism that is associated with lepromatous leprosy is unable to mediate mycobacterial signaling

Toll-like receptors (TLRs) are key mediators of the innate immune response to microbial pathogens. We investigated the role of TLRs in the recognition of Mycobacterium leprae and the significance of TLR2Arg(677)Trp, a recently discovered human polymorphism that is associated with lepromatous leprosy. In mice, TNF-alpha production in response to M. leprae was essentially absent in TLR2-deficient macrophages. Similarly, human TLR2 mediated M. leprae-dependent activation of NF-kappaB in transfected Chinese hamster ovary and human embryonic kidney 293 cells, with enhancement of this signaling in the presence of CD14. In contrast, activation of NF-kappaB by human TLR2Arg(677)Trp was abolished in response to M. leprae and Mycobacterium tuberculosis. The impaired function of this TLR2 variant provides a molecular mechanism for the poor cellular immune response associated with lepromatous leprosy and may have important implications for understanding the pathogenesis of other mycobacterial infections.     

Effect of recombinant interferon-gamma on hydrogen peroxide-releasing capacity of monocyte-derived macrophages from patients with lepromatous leprosy

Monocyte-derived macrophages from 14 patients with lepromatous leprosy respond to rIFN-gamma with an enhanced secretion of H2O2 in a fashion similar to that of cells obtained from normal donors. The activation is not dependent on the cutaneous bacterial index, the length of treatment, or the stage and activity of the disease. H2O2 release can be triggered in these cells both by phorbol myristate acetate and by intact irradiated Mycobacterium leprae. Uptake of M. leprae by both normal donors' and patients' macrophages is proportional to the number of bacilli added. Prior ingestion of M. leprae does not interfere with the ability of macrophages to respond to IFN-gamma by the production of oxygen intermediates. We conclude that the immune defect in lepromatous leprosy probably results from a lack of response to M. leprae by the patients' T cells rather than an inability of mononuclear phagocytes to respond to IFN-gamma.     

Production of lymphokines by circulating human T lymphocytes that express or lack receptors for interleukin 2

The capacity for circulating human T cells which have or lack receptors for interleukin 2 (IL 2) to produce IL 2, interleukin 3 (IL 3), and interferon-gamma (IFN-gamma) under the stimulus of phytohemagglutinin was studied. By using the monoclonal anti-Tac antibody which reacts against IL 2 receptors on human T cells, concanavalin A-treated T cells were separated into IL 2 receptor-positive (Tac+ T cells) and IL 2 receptor-negative (Tac- T cells) lymphocytes. The results show that Tac+ T cells secreted IL 2 and IFN-gamma but not IL 3. Tac- T cells produced IL 2 and IL 3 but not IFN-gamma. It is concluded that: 1) both T cells lacking and T cells having receptors for IL 2 produce IL 2, but only IL 2 receptor-negative T cells appear to secrete IL 3; and 2) virtually all of the T cells that produce IFN-gamma after PHA stimulation express receptors for IL 2.     

Bacterial lipopolysaccharide-induced interferon-gamma production: roles of interleukin 1 and interleukin 2

Bacterial lipopolysaccharide (LPS) induced human peripheral blood mononuclear cells (PBMC) to produce interferon-gamma (IFN-gamma). Monocytes play a mandatory accessory role in this process, because purified T lymphocytes failed to produce IFN-gamma in response to LPS and the addition of 2% monocytes to T cell cultures resulted in an optimal LPS-induced IFN-gamma production. IFN-gamma production was abolished in the presence of monoclonal antibodies specific for HLA-DR antigen. Addition of exogenous interleukin 2 (IL 2) markedly enhanced IFN-gamma secretion by PBMC induced with LPS. The addition of anti-Tac antibody specific for IL 2 receptors abrogated IFN-gamma production, suggesting that an interaction of IL 2 with IL 2 receptors was involved. By using a specific antibody binding assay, LPS was shown to amplify IL 2 receptor expression on PBMC, whereas exogenous IL 2 showed only a negligible enhancing effect on the expression of its own receptors. Interleukin 1 (IL 1), a product of LPS-stimulated monocytes, potentiated IL 2-induced IFN-gamma production in the absence of LPS. Neither IL 1 nor IL 2 alone induced IFN-gamma production in purified T lymphocyte cultures. When added together, however, substantial levels of IFN-gamma were induced. An enhanced IL 2 receptor expression on T cells was also demonstrated as a result of the combined action of IL 1 and IL 2. These results suggest that induction of IFN-gamma by LPS is due mainly to the generation of IL 1 and an enhanced expression of IL 2 receptors.     

Response to and production of interleukin 2 by peripheral blood and cerebrospinal fluid lymphocytes of patients with multiple sclerosis

In an effort to further characterize the defective proliferative response of T lymphocytes to mitogens in multiple sclerosis (MS) patients, we examined the response to and production of interleukin 2 (IL 2) by both peripheral blood lymphocytes (PBL) and cerebrospinal fluid mononuclear cells. We also examined the proportion of cells bearing receptors for IL 2 and transferrin. Chronic progressive MS patients have an abnormally low response to exogenous IL 2 as compared to controls. Whereas acute relapse patients' PBL demonstrated a normal IL 2 response during an exacerbation, they showed reduced responsiveness during remission. These abnormalities could not be explained by different dose or kinetic response optima to PHA or IL 2, nor could they be explained by depressed numbers of IL 2 or transferrin receptor-bearing lymphocytes. Production of IL 2 by PBL was also abnormal in MS patients. Chronic progressive patients produced elevated levels of IL 2, whereas acute relapse patients undergoing an exacerbation produced diminished levels of IL 2. During remission, these levels returned to that of controls'. The effect of 1200 rad x-irradiation or nylon wool removal of adherent cells was a significantly greater augmentation of IL 2 production in MS patients than in other neurologic disease or normal controls. Cerebrospinal fluid lymphocytes from MS patients had normal proportions of IL 2 receptor-bearing cells, but were deficient in their IL 2 response and production as compared to autochthonous or control PBL. The inability of some MS patients' lymphocytes to clonally expand in response to IL 2 might contribute to the pathogenicity of the disease.     

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.     

Reciprocity between Regulatory T Cells and Th17 Cells: Relevance to Polarized Immunity in Leprosy

T cell defect is a common feature in lepromatous or borderline lepromatous leprosy (LL/BL) patients in contrast to tuberculoid or borderline tuberculoid type (TT/BT) patients. Tuberculoid leprosy is characterized by strong Th1-type cell response with localized lesions whereas lepromatous leprosy is hallmarked by its selective Mycobacterium leprae specific T cell anergy leading to disseminated and progressive disease. FoxP3+ Regulatory T cells (Treg) which are essential for maintaining peripheral tolerance, preventing autoimmune diseases and limiting chronic inflammatory diseases also dampen proinflammatory T cells that include T helper 17 (Th17) cells. This study is aimed at evaluating the role of Treg cells in influencing other effector T cells and its relationship with the cytokine polarized state in leprosy patients. Peripheral blood mononuclear cells from of BT/TT (n = 15) and BL/LL (n = 15) patients were stimulated with M. leprae antigen (WCL) in presence of golgi transport inhibitor monensin for FACS based intracellular cytokine estimation. The frequency of Treg cells showed >5-fold increase in BL/LL in comparison to BT/TT and healthy contacts. These cells produced suppressive cytokine, IL-10 in BL/LL as opposed to BT/TT (p = 0.0200) indicating their suppressive function. The frequency of Th17 cells (CD4, CD45RO, IL-17) was, however, higher in BT/TT. Significant negative correlation (r = -0.68, P = 0.03) was also found between IL-10 of Treg cells and IL-17+ T cells in BL/LL. Blocking IL-10/TGF-β restored the IL-17+ T cells in BL/LL patients. Simultaneously, presence of Th17 related cytokines (TGF-β, IL-6, IL-17 and IL-23) decreased the number of FoxP3+ Treg cells concomitantly increasing IL-17 producing CD4+ cells in lepromatous leprosy. Higher frequency of Programmed Death-1/PD-1+ Treg cells and its ligand, PDL-1 in antigen presenting cells (APCs) was found in BL/LL patients. Inhibition of this pathway led to rescue of IFN-γ and IL-17 producing T cells. Results indicate that Treg cells are largely responsible for the kind of immunosuppression observed in BL/LL patients. This study also proves that Treg cells are profoundly affected by the cytokine milieu and this property may be utilized for benefit of the host.     

Lyt-2+ cells. Requirements for concanavalin A-induced proliferation and interleukin 2 production

The requirements for inducing Lyt-2+ T cell proliferation in response to concanavalin A (Con A) were examined. Purified Lyt-2+ or L3T4+ spleen cells of C57BL/6 origin were stimulated with Con A and syngeneic macrophages (MO) in the presence of monoclonal antibodies to T cell markers or to polymorphic determinants on major histocompatibility complex molecules, and assessed for the ability to proliferate and to produce interleukin (IL) 2. alpha I-Ab failed to inhibit the Con A response of Lyt-2+ cells at dilutions that significantly inhibited the response of L3T4+ cells. In contrast, alphaKb/Db or alpha Lyt-2.2 specifically inhibited the response of Lyt-2+ cells, but not L3T4+ cells. The ability of alpha Kb/Db and of alpha Lyt-2.2 to inhibit the response of Lyt-2+ cells was dependent upon the concentration of Con A. These data demonstrate that optimal triggering of T cell subsets to proliferate and to produce IL-2 in response to Con A requires interactions with the appropriate restricting major histocompatibility complex molecule. The role of accessory cells in Lyt-2+ Con A-induced proliferation and IL-2 production was also investigated. Purified Lyt-2+ cells and purified L3T4+ cells failed to respond to Con A in the absence of MO. IL-1 reconstituted the response when MO were limiting, but failed to restore the response of either Lyt-2+ or L3T4+ cells when T cells were rigorously purified to remove all MO. These results demonstrate that triggering Lyt-2+ T cells, like L3T4+ T cells, requires accessory cells, and that this does not merely reflect a requirement for IL-1 production. Thus, Con A-induced proliferation and IL-2 production by Lyt-2+ T cells requires intimate contact with accessory cells and interactions dependent upon the class I-restricting element.     

Signaling lymphocytic activation molecule expression and regulation in human intracellular infection correlate with Th1 cytokine patterns.

Induction of Th1 cytokines, those associated with cell-mediated immunity, is critical for host defense against infection by intracellular pathogens, including mycobacteria. Signaling lymphocytic activation molecule (SLAM, CD150) is a transmembrane protein expressed on lymphocytes that promotes T cell proliferation and IFN-gamma production. The expression and role of SLAM in human infectious disease were investigated using leprosy as a model. We found that SLAM mRNA and protein were more strongly expressed in skin lesions of tuberculoid patients, those with measurable CMI to the pathogen, Mycobacterium leprae, compared with lepromatous patients, who have weak CMI against M. leprae. Peripheral blood T cells from tuberculoid patients showed a striking increase in the level of SLAM expression after stimulation with M. leprae, whereas the expression of SLAM on T cells from lepromatous patients show little change by M. leprae stimulation. Engagement of SLAM by an agonistic mAb up-regulated IFN-gamma production from tuberculoid patients and slightly increased the levels of IFN-gamma in lepromatous patients. In addition, IFN-gamma augmented SLAM expression on M. leprae-stimulated peripheral blood T cells from leprosy patients. Signaling through SLAM after IFN-gamma treatment of Ag-stimulated cells enhanced IFN-gamma production in lepromatous patients to the levels of tuberculoid patients. Our data suggest that the local release of IFN-gamma by M. leprae-activated T cells in tuberculoid leprosy lesions leads to up-regulation of SLAM expression. Ligation of SLAM augments IFN-gamma production in the local microenvironment, creating a positive feedback loop. Failure of T cells from lepromatous leprosy patients to produce IFN-gamma in response to M. leprae contributes to reduced expression of SLAM. Therefore, the activation of SLAM may promote the cell-mediated immune response to intracellular bacterial pathogens.     

Experimental visceral leishmaniasis: production of interleukin 2 and interferon-gamma, tissue immune reaction, and response to treatment with interleukin 2 and interferon-gamma

During the first 2 to 4 weeks of progressive visceral infection with the intracellular protozoan, Leishmania donovani, spleen cells from BALB/c mice failed in response to leishmanial antigen to produce either of the activating T cell-derived lymphokines, interleukin 2 (IL 2) or gamma-interferon (IFN-gamma). Four weeks after infection, however, antigen-induced IL 2 and IFN-gamma secretion emerged and coincided with the onset of control over parasite replication and the subsequent killing of greater than 80% of intrahepatic L. donovani. The development of this immunosecretory activity correlated with the hepatic tissue response at the site of parasitized Kupffer cells. This response progressed from Kupffer cell fusion (week 1) to fusion plus a mononuclear cell infiltrate (week 2) to well-organized granuloma formation (weeks 4 to 8). In contrast, T cell-deficient nude BALB/c mice exerted no control over L. donovani, their spleen cells failed to generate antigen-induced IFN-gamma, and at 4 weeks, their livers were devoid of any tissue reaction. Since spleen cells from 2-week infected normal mice did not produce antigen-stimulated IL 2 or IFN-gamma, these mice were treated with recombinant (r) lymphokines. Various protocols using both high and low dose human rIL 2 had no antileishmanial effect. Hepatic parasite replication was completely halted, however, by macrophage-activating doses of murine rIFN-gamma. These results reemphasize that an intact T cell-dependent response is required for successful defense against L. donovani, indicate that this immune response can be measured at both the cellular (secretory) and tissue levels, and confirm that IFN-gamma can exert an antileishmanial effect in vivo.     

Characterization of T lymphocyte subpopulations responsible for deficient interleukin 2 activity in patients with systemic lupus erythematosus

Normal immunoregulation depends on a complex set of cellular interactions in which interleukin 2 (IL 2) appears to play an important role. We have examined the IL 2 activity in patients with systemic lupus erythematosus (SLE). IL 2 production by phytohemagglutinin (PHA)-stimulated T cells for 48 hr was measured by the ability of their culture fluid to induce proliferation of normal human T cells that had been activated for more than 20 days by PHA plus IL 2. To measure IL 2 responsiveness, T cells were blasted by preincubation with concanavalin A for 96 hr and stimulated for another 72 hr with lectin-free standard IL 2. SLE T cells failed to produce normal levels of IL 2 in vitro compared with normal control T cells. This failure resided in both OKT4+ and OKT8+ cells. Furthermore, the abnormality was due neither to soluble inhibitory factors produced by SLE T cells nor to active suppressor cells that might be induced by PHA-stimulation. Responsiveness to IL 2 of T cells from some, but not all, SLE patients was decreased significantly from that of normal controls. Absorption studies as well as studies with anti-Tac antibody demonstrated that the impaired responsiveness of T cells in the specific patients with SLE was due to inadequate expression of IL 2 receptors on the T cells upon activation. This defect was exclusively ascribed to the dysfunction of OKT4+, but not OKT8+, cells. The above defects in production of and responsiveness to IL 2 observed in patients with SLE were present at all times regardless of the disease activity or of corticosteroid therapy. Thus, the deficient IL 2 activity may be intrinsic to SLE lymphocytes and may contribute to impaired immunoregulation and to the development of SLE.