Thymic Activity Research Articles

Molecular and supra-molecular structure related differences in toxicity and granulomatogenic activity of mycobacterial cord factor in mice

To establish the structure biological activity relationship of cord factor (trehalose 6,6′-dimycolate, TDM), we compared the molecular or supra-molecular structure of TDM micelles with toxicity, thymic atrophy and granulomatogenicity in lungs and spleen of BALB/c mice. According to the difference in the mycolyl subclass composition, TDM was divided into two groups, one possessing α-, methoxy- and keto-mycolates in M. tuberculosis H 37Rv, M. bovis BCG and M. kansasii (group A) and the other having α-, keto- and wax ester-mycolates in M. avium serotype 4, M. phlei and M. flavescens (group B), although mycolic acid molecular species composition differed in each group considerably. Supra-molecular structure of TDM micelle differed species to species substantially and the micelle size of TDM from M. bovis BCG Connaught was the largest. The highest toxicity was shown with TDM from M. tuberculosis H 37Rv which possessed the highest amount of α- (47.3%) and methoxy-mycolates (40.8%), while TDM from M. phlei having the low amount of α-mycolate (11.6%) showed almost no toxicity with the given doses. The thymic atrophy was observed with TDM from group A, but not with TDM from group B. On the other hand, TDM from group B showed massive lung granulomatogenic activity based on the histological observations and organ indices. Taken together, group A TDM showed a wide variety of micelle sizes and specific surface areas, high to low toxicity and marked to moderate granulomatogenicity, while group B TDM showed smaller sizes of micelles and larger specific surface areas, lower toxicity but higher granulomatogenicity in lungs. Existence of higher amount of longer chain α-mycolates in TDM appeared to be essential for high toxicity and thymic apoptotic activity, whereas TDM possessing wax ester-mycolate with smaller sized micelles seemed to be less toxic, but more granulomatogenic in lungs in mice. Thus, the mycolic acid subclass and molecular species composition of TDM affect critically the micelle forms, toxicity and granulomatogenicity in mice, while the relative abundances and carbon chain length of α-mycolate affected the toxicity in mice.

Aging and T-cell diversity

Naïve and memory CD4 and CD8 T cells constitute a highly dynamic system with constant homeostatic and antigen-driven proliferation, influx, and loss of T cells. Thymic activity dwindles with age and essentially ceases in the later decades of life, severely constraining the generation of new T cells. Homeostatic control mechanisms are very effective at maintaining a large and diverse subset of naïve CD4 T cells through the 7th decade of life, but eventually and abruptly fail at about the age of 75 years. In contrast, the CD8 T cell compartment is more unstable, with progressive diminution of naïve T cells and increasing loss of diversity during mid adulthood. Vaccination strategies need to aim at developing a broad repertoire of memory T cells before the critical time period when the naïve CD4 T-cell repertoire collapses. Research efforts need to aim at understanding T-cell homeostatic control mechanisms to ultimately expand the time period of repertoire stability.

Circulating levels of IL-7 in rheumatoid arthritis

We have previously demonstrated reduced circulating levels of IL-7 in active rheumatoid arthritis (RA) compared with health [1]. Controversy exist as to whether IL-7 correlates or not with C-reactive protein (CRP) in active disease or with other disease activity markers. Normal IL-7 levels were, however, found in 50% of patients in clinical remission and correlated with the recovery of thymic activity [1]. Patients in clinical remission may represent a heterogeneous group, and the aim of this work was to identify predictors of IL-7 recovery in demographic, clinical, imaging and functional data and to compare them with IL-7 in active disease. One hundred and six patients deemed to be in clinical remission were recruited: stable disease for the preceding 6 months, previous disease duration of at least 12 months, no clinically significant synovitis, CRP below 15 mg/l for the preceding 6 months. Blood and serum were collected from these patients (n = 106). Clinical data and imaging data were gathered at the time of sampling. High-sensitivity ELISA was used for cytokine analysis, proliferation assays for T-cell function (mitogen, T-cell receptor stimulation, IL-2, recall antigens); real-time PCR to quantify T-bet and GATA3 expression, and DNA sequencing was carried out to investigate two genetic polymorphisms in the IL-7 gene. Several studies in healthy controls indicate that normal levels of circulating IL-7 are between 10 and 25 pg/ml. In remission, circulating levels of IL-7 vary between 2.47 and 23.85 pg/ml. Recovery of T-cell function was directly related to levels of circulating IL-7 in vivo (P < 0.001, R = 0.873 for phytohaemagglutinin, R = 0.786 for T-cell receptor stimulation and R = 0.821 for recall antigen). Age and sex had no effect on IL-7. Combining active (n = 35) and remission patients (n = 106) showed no indication of a relationship between IL-7 and routine measures of disease activity (CRP, DAS28, erythrocyte sedimentation rate, plasma viscosity and joint counts), suggesting that recovery of IL-7 is not an indicator of remission. To confirm this observation, we used imaging data (MRI and US assessment of hand and wrist) to address whether subclinical disease could predict lack of IL-7 recovery. Evidence of subclinical synovitis was found in 96% of patients in remission [2] despite no evidence of clinically significant synovitis and there was no relationship between IL-7 and imaging scores. However, we found that levels of IL-7 in remission and the age of the patient at disease onset correlate (P < 0.001, R = 0.498, n = 86). A family history of RA and smoking at the time of onset (both self-reported) were also strongly associated with lower levels of IL-7 (both P < 0.001, n = 66). We analysed two polymorphisms in the promoter and enhancer regions of the IL-7 gene. We found no allele frequency difference between RA patients and healthy controls, remission patients with or without family history, or in relation to IL-7 levels. Finally we analysed circulating cytokines known to regulate IL-7 expression, and found a strong correlation between IL-7 and IFNγ (P < 0.03, R = 0.650, n = 10). Since IL-7 is a co-activator of Th1 polarisation, we analysed the expression of T-bet and found a direct relationship between the two (P < 0.01, R = 0.601, n = 15) but not with GATA3, which is a regulator of Th2 polarisation. Recent evidence suggests an important role for IL-7 in the pathogenesis of RA [3]. Our data demonstrate that circulating IL-7 is not an indicator of disease activity. Despite the relationship with age at onset (genetic anticipation) and the family history association, levels of IL-7 in the circulation are apparently not driven by these two polymorphisms. Our results suggest that Th1 polarisation and IL-7 are related and that the mechanism by which IL-7 is recovered in remission may be associated with the recovery of Th1 polarisation.

Plasticity of neuroendocrine–thymus interactions during ontogeny and ageing: Role of zinc and arginine

Thymic re-growth and reactivation of thymic functions may be achieved in old animals by different endocrinological or nutritional manipulations such as, (a) treatment with melatonin, (b) implantation of a growth hormone (GH) secreting tumour cell line (GH3 cells) or treatment with exogenous GH, (c) castration or treatment with exogenous luteinizing hormone-releasing hormone (LHRH), (d) treatment with exogenous thyroxin or triiodothyronine, and (e) nutritional interventions such as arginine or zinc supplementation. These data strongly suggest that thymic involution is a phenomenon secondary to age-related alterations in neuroendocrine–thymus interactions and that it is the disruption of these interactions in old age that is responsible for age-associated immune–neuroendocrine dysfunctions. The targets involved in hormones-induced thymic reconstitution may directly or indirectly involve hormone receptors, cytokines, arginine, and a trace element such as zinc, which is pivotal for the efficiency of neuroendocrine–immune network during the whole life of an organism. The effect of GH, thyroid hormones, and LHRH may be due to specific hormone receptors on thymocytes and on thymic epithelial cells (TECs), which synthesize thymic peptides. Melatonin may also act through specific receptors on T-cells. In this context, the role of zinc, which turnover is reduced in old age, is pivotal because of its involvement through zinc fingers in the gene expression of hormone receptors. In addition, the effects of zinc are multifaceted: from the reactivation of zinc-dependent enzymes, to cell proliferation and apoptosis, to cytokines expression and to the reactivation of thymulin, which is a zinc-dependent thymic hormone required for intrathymic T-cell differentiation and maturation as well as for the homing of stem cells into the thymus. Zinc is also required for arginine action, via NO pathway. The role of zinc is therefore crucial in neuroendocrine–thymus interactions. According to data in animals and humans, the above reported endocrinological manipulations (GH, thyroid hormones, and melatonin) or arginine treatment may also act via zinc pool in restoring thymic activity in ageing allowing improvements on peripheral immune efficiency.

Thymic volume, T-cell populations, and parameters of thymopoiesis in adolescent and adult survivors of HIV infection acquired in infancy

Antiretroviral therapy has significantly prolonged the lifespan of children who acquire HIV infection in infancy, but the impact of HIV on thymus-mediated maintenance of T lymphocytes has not been studied. To examine the long-term effects of HIV infection in childhood on thymopoiesis, thymic volume and parameters of thymic function from clinically stable adolescents and young adults with HIV infection acquired in infancy were compared with those from uninfected controls. Thymic volume was determined using three-dimensional reconstruction and volumetric analysis of non-contrast enhanced computed tomography images of the upper chest. The degree of fat involution was assessed using a semiquantitive scoring system. CD4 and CD8 T cell populations and T cell receptor recombination excision circles (TREC) concentrations in peripheral blood lymphocytes were measured in all subjects. Twenty youths (aged 17.6 +/- 2.5 years) with HIV infection acquired perinatally (n = 18) or by neonatal transfusion (n = 2) were enrolled whose HIV plasma viral load had been undetectable for a median of 3.1 years, along with 18 seronegative healthy young adults (aged 20.6 +/- 1.3 years). HIV infected subjects and controls had indistinguishable CD4 T cell counts, thymus volumes (20.5 versus 15.8 cm), thymic index scores, and TREC values. Thymic volume correlated with the number and percentage of CD4 T lymphocytes in the control group and with the number of TREC in CD4 lymphocytes in the HIV infected group. Long term survivors of pediatric HIV infection appear to have retained or recovered thymic volume and thymic activity approximating uninfected youths.

High Expression of Antioxidant Proteins in Dendritic Cells

Dendritic cells (DCs) display the unique ability to activate naive T cells and to initiate primary T cell responses revealed in DC-T cell alloreactions. DCs frequently operate under stress conditions. Oxidative stress enhances the production of inflammatory cytokines by DCs. We performed a proteomic analysis to see which major changes occur, at the protein expression level, during DC differentiation and maturation. Comparative two-dimensional gel analysis of the monocyte, immature DC, and mature DC stages was performed. Manganese superoxide dismutase (Mn-SOD) reached 0.7% of the gel-displayed proteins at the mature DC stage. This important amount of Mn-SOD is a primary antioxidant defense system against superoxide radicals, but its product, H(2)O(2), is also deleterious for cells. Peroxiredoxin (Prx) enzymes play an important role in eliminating such peroxide. Prx1 expression level continuously increased during DC differentiation and maturation, whereas Prx6 continuously decreased, and Prx2 peaked at the immature DC stage. As a consequence, DCs were more resistant than monocytes to apoptosis induced by high amounts of oxidized low density lipoproteins containing toxic organic peroxides and hydrogen peroxide. Furthermore DC-stimulated T cells produced high levels of receptor activator of nuclear factor kappaB ligand, a chemotactic and survival factor for monocytes and DCs. This study provides insights into the original ability of DCs to express very high levels of antioxidant enzymes such as Mn-SOD and Prx1, to detoxify oxidized low density lipoproteins, and to induce high levels of receptor activator of nuclear factor kappaB ligand by the T cells they activate and further emphasizes the role that DCs might play in atherosclerosis, a pathology recognized as a chronic inflammatory disorder.

Androgen Modulates Thymopoiesis by Regulating Thymocyte Precursor Immigration.

Impaired thymopoiesis contributes to immune deficiency in aging, AIDS, and following allogeneic bone marrow transplantation. However, little is known of the mechanisms of thymic regulation and the determinants of thymic function. Exogenous administration of testosterone and estrogen has been shown to accelerate thymic involution. Conversely, studies have demonstrated that castration of male mice resulted in increased thymic size and thymocyte number. We present data that thymic enlargement in castrated male mice is due to enhanced thymopoiesis. Comparing castrated post-pubertal male mice with age-matched control littermates, we found a statistically significant doubling of thymic weight, thymocyte number, and double-positive CD4+CD8+ thymocytes as early as eight days post-orchiectomy. Major thymocyte subsets defined as CD4− CD8−, CD4+CD8−, CD8+CD4− were also increased post castration and the ratio of subsets was unchanged suggesting that castration augmented overall thymic activity. This was further corroborated by a concomitant 4–6 fold increase in thymic T cell-receptor excision circles (TREC). Significantly, at one month post-castration, early thymic progenitors (Lin- CKIT hi CD44 hi) were increased threefold in the castrated cohort. The increase in thymic productivity led to a subsequent increase in peripheral cell populations, with a significant increase in splenic CD4+ and CD8+ T cells. The greatest proportion of this increase was due to naïve splenic CD4 and CD8 T cells total numbers as defined by CD44lo expression. Memory splenocytes, CD44hi CD4+ and CD8+ cells, were slightly increased as well. Additionally, there was an increase in the number of splenic recent thymic emigrants (RTE) as enumerated by TREC. Our data suggest that androgen withdrawal leads to an increase in thymopoiesis, as enumerated by a significant influx of ETPs, increased total thymic TREC, subsequent increases in single positive thymocytes, and increased peripheral recent thymic emigrants. Furthermore, the data suggest that a mechanism by which this occurs is through increased immigration of thymocyte precursors from the bone marrow into the thymus identifying this as a central point in thymic regulation.

In vitro and in vivo effects of mercuric chloride on thymic endocrine activity, NK and NKT cell cytotoxicity, cytokine profiles (IL-2, IFN-γ, IL-6): Role of the nitric oxide-l-arginine pathway

Mercury (Hg2+) affects cell-mediated immunity, including thymulin production. Thymulin, a zinc-dependent thymic hormone synthesized by thymic epithelial cells (TECs), is involved in NK cell cytotoxicity and Th1 cytokine production (IL-2 and IFN-γ), which in turn affect both NKT and classic NK spleen cell cytotoxicity. High doses of Hg2+ induce an inflammatory status, increased production of IL-6 and consequent Th1/Th2 imbalance as well as cell-mediated immune depression. The mechanisms by which Hg+ affects the cell-mediated immune response are still unclear. The nitric oxide (NO) pathway may be implicated. The aim of this work was to further explore its noxious role in innate and adaptive immunity and to study the possible role played by the NO pathway. Young Balb/c mice treated in vivo for 1 month with 1.0 mg HgCl2/kg b.w. showed low thymulin activity, depressed NO production (as measured by nitrite and nitrate plasma levels), impaired classic NK spleen cell cytotoxicity, decreased Th1 (IL-2 and IFN-γ) cytokine profiles, and increased IL-6 production. In vitro, 10−6 M of HgCl2 inhibited active thymulin kinetics, TEC proliferation, NKT cell cytotoxicity and Th1 cytokine production, whereas IL-6 increased. l-arginine restored thymulin activity, TEC proliferation, NKT cytotoxicity, cytokine profiles and nitrite and nitrate plasma levels both in vivo and in vitro. Since l-arginine is the substrate for NO production, it may compensate for the cell-mediated immune defect induced by HgCl2, via the arginine-NO-pathway. l-arginine is also able to reduce glomerular kidney IgG antibodies deposits induced by higher dose of HgCl2 administration.

Essential oil composition and antioxidant activity ofThymus bracteosus Vis. ex Benth.

The composition of the essential oil and the antioxidant properties of the dried herbs of Thymus bracteosus Vis. ex Benth. (Lamiaceae) were investigated. Of the essential oil (yield 0.06%), 77.4% could be identified by GC[sol ]MS analysis. The major compounds were germacrene-D (11.6%), β-caryophyllene (9.7%), myrcene (7.2%), α-pinene (6.3%) and trans-β-farnesene (6.1%). The content of thymol was very low (0.1%) as compared with the essential oil of T. vulgaris. Aqueous and methanolic extracts as well as the essential oil of T. bracteosus were also investigated on their radical scavenger capacity. Furthermore, the ability of the extracts to inhibit peroxidation of membrane lipids was tested. The essential oil of T. bracteosus did not show any antioxidant activity in the test systems. Copyright © 2005 John Wiley & Sons, Ltd.

Precocious aging of the immune system in Down syndrome: Alteration of b lymphocytes, T-lymphocyte subsets, and cells with natural killer markers

Phenotype and proliferative ability of peripheral blood lymphocytes from 15 noninstitutionalized children affected with Down Syndrome (DS), in apparently good health, were studied and compared with those of 16 healthy control children of the same age. A complex derangement of all the major peripheral blood cell subsets, i.e., B cells, T cells, and natural killer (NK) cells, was present in DS children. A significant decrease of the absolute number of circulating lymphocytes, a marked and significant decrease of B lymphocyte absolute number and percentage, and dramatic modifications of the T-cell subsets were observed. The absolute number of CD4+ cells was significantly decreased, whereas CD8+ cells increased significantly in percentage but not in absolute number. A derangement of cells bearing markers associated with NK activity, such as CD57, CD16, and CD56, was observed. Among the most important alterations, the presence of a high number of CD57+, CD16- cells, of CD57+, CD8+ lymphocytes, and of CD3+, CD56+ lymphocytes was seen. Many of these alterations are similar to those characteristic of chromosomally normal subjects of advanced age. The hypothesis that the reduced thymic endocrine activity and the zinc deficiency characteristic of DS are responsible for the derangement of T and NK subsets is discussed.

Age‐related thymic activity in adults following chemotherapy‐induced lymphopenia

The potential role of the adult thymus in T-cell homeostasis subsequent to lymphopenia remains the subject of debate. We examined whether thymic activity contributes to reconstitution of the peripheral T-cell pool, a critical process for patients recovering from antineoplastic therapy. In selected patients with various neoplastic diseases we assessed peripheral blood lymphocyte subsets by flow-cytometry, including thymus-derived, CD4+ T cells expressing the CD45RA molecule, and thymic size rebound by CT scan before, and 3, 6 and 12 months after completion of cytotoxic therapy. Adult patients (n = 21, mean age of 30 years, range 18-49) had higher baseline numbers of B and lower numbers of NK cells than elderly patients (n = 15, mean age of 79 years, range 70-91), while total T-cell numbers did not differ. Despite the reduction of lymphocyte counts being comparable in the adult (mean of 45%) and elderly (mean of 49%) groups, occurring at, or near, completion of treatment, an enlargement of the previously atrophic thymus was evident in 63% of the adult, but in none of the elderly, subjects. In 22 patients who remained active disease-free during the following year, B cells and NK cells recovered to pretreatment levels as soon as at 3 months, whereas overall T-cell recovery occurred at 6 months post-treatment. Thymic rebound, observed in 11 of 22 patients who were of younger age, correlated significantly with a faster and more complete recovery of CD45RA+ CD4+ (mainly helper-naïve) T cells. The adult thymus appears capable of regeneration, at least up to middle age, contributing significantly to the reconstitution of the peripheral T-cell pool following chemotherapy-induced lymphopenia. In advanced age, however, although peripheral homeostatic pathways appear intact, regeneration of the naïve repertoire is incomplete.

Insights into thymic aging and regeneration

The deterioration of the immune system with progressive aging is believed to contribute to morbidity and mortality in elderly humans due to the increased incidence of infection, autoimmunity, and cancer. Dysregulation of T-cell function is thought to play a critical part in these processes. One of the consequences of an aging immune system is the process termed thymic involution, where the thymus undergoes a progressive reduction in size due to profound changes in its anatomy associated with loss of thymic epithelial cells and a decrease in thymopoiesis. This decline in the output of newly developed T cells results in diminished numbers of circulating naive T cells and impaired cell-mediated immunity. A number of theories have been forwarded to explain this 'thymic menopause' including the possible loss of thymic progenitors or epithelial cells, a diminished capacity to rearrange T-cell receptor genes and alterations in the production of growth factors and hormones. Although to date no interventions fully restore thymic function in the aging host, systemic administration of various cytokines and hormones or bone marrow transplantation have resulted in increased thymic activity and T-cell output with age. In this review, we shall examine the current literature on thymic involution and discuss several interventional strategies currently being explored to restore thymic function in elderly subjects.

Onset of thymic recovery and plateau of thymic output are differentially regulated after stem cell transplantation in children

Thymus-dependent T-cell regeneration is a major pathway for immune reconstitution after stem cell transplantation in children. Therefore, we prospectively assessed T-cell dynamics and thymic function in 164 pediatric patients between 1 and 124 months after transplantation by measuring T-cell receptor recombination excision circles and spontaneous expression of Ki67 in peripheral T-cell subsets. We analyzed the effect of recipient age, conditioning regimen, type of donor and graft, stem cell dose, and graft-versus-host disease on the onset and the plateau of thymic output. A high rate of spontaneous proliferation in early-reconstituting naive and memory T cells inversely correlated with total T-cell numbers. Accordingly, T-cell receptor recombination excision circle content was diminished in early-appearing naive T cells. A multivariate analysis revealed that the onset of thymic recovery was inversely correlated only with recipient age ( P < .0002), whereas the plateau of thymic output was higher in patients receiving increased stem cell numbers ( P < .0022). Donor type, stem cell source, and conditioning regimen influenced none of the analyzed parameters. In conclusion, lymphopenia-driven proliferation is important for T-cell homeostasis in children early after stem cell transplantation, but it might result in underestimation of thymic function. Onset and plateau of thymic activity are independently regulated by different transplant-related factors.

Thymic activity of human growth hormone on murine thymocytes: Potential role in promoting thymopoiesis following bone marrow transplant

Thus far, very few agents have been demonstrated to positively affect thymic function. Many cytokines have been shown to promote peripheral T cell function but only a select few (i.e. IL-7 and SCF) have been shown to promote thymopoiesis or T progenitor cell survival. Most cytokines were meant to exert local effects and it is often difficult to generate the levels needed after systemic administration to yield sustained biological effects. Hormones, by their very nature, are well suited for systemic administration.

Thymus is Enlarged in Children with Current Atopic Dermatitis. A Cross-sectional Study

Atopic dermatitis is a common skin disorder of unknown aetiology with peak incidence in early childhood. The disease is associated with peripheral T-cell accumulation in the skin. The thymus is a key organ of the cellular immune response early in life. We hypothesized that atopic dermatitis is associated with an unbalanced establishment of the peripheral T-lymphocyte system. This cross-sectional study was performed to compare thymus sizes in patients with atopic dermatitis and healthy controls. Thirty-seven children with current atopic dermatitis were enrolled and compared with 29 healthy controls. An interview and medical examination were performed by one doctor, an ultrasound scan was performed within 3 days of the examination, and the thymus index, a marker of thymus size, was measured. The thymus index was on average 32% higher (95% CI 3%-67%) in children with active atopic dermatitis compared with healthy controls. It declined with age in both children with atopic dermatitis and healthy controls, but the reduction in size was only significant for healthy controls. We demonstrate increased size of thymus among children with active atopic dermatitis compared with healthy controls. The larger size of thymus is compatible with increased thymic activity and emission of T lymphocytes.

Interleukin-7 deficiency in rheumatoid arthritis: consequences for therapy-induced lymphopenia

We previously demonstrated prolonged, profound CD4+ T-lymphopenia in rheumatoid arthritis (RA) patients following lymphocyte-depleting therapy. Poor reconstitution could result either from reduced de novo T-cell production through the thymus or from poor peripheral expansion of residual T-cells. Interleukin-7 (IL-7) is known to stimulate the thymus to produce new T-cells and to allow circulating mature T-cells to expand, thereby playing a critical role in T-cell homeostasis. In the present study we demonstrated reduced levels of circulating IL-7 in a cross-section of RA patients. IL-7 production by bone marrow stromal cell cultures was also compromised in RA. To investigate whether such an IL-7 deficiency could account for the prolonged lymphopenia observed in RA following therapeutic lymphodepletion, we compared RA patients and patients with solid cancers treated with high-dose chemotherapy and autologous progenitor cell rescue. Chemotherapy rendered all patients similarly lymphopenic, but this was sustained in RA patients at 12 months, as compared with the reconstitution that occurred in cancer patients by 3–4 months. Both cohorts produced naïve T-cells containing T-cell receptor excision circles. The main distinguishing feature between the groups was a failure to expand peripheral T-cells in RA, particularly memory cells during the first 3 months after treatment. Most importantly, there was no increase in serum IL-7 levels in RA, as compared with a fourfold rise in non-RA control individuals at the time of lymphopenia. Our data therefore suggest that RA patients are relatively IL-7 deficient and that this deficiency is likely to be an important contributing factor to poor early T-cell reconstitution in RA following therapeutic lymphodepletion. Furthermore, in RA patients with stable, well controlled disease, IL-7 levels were positively correlated with the T-cell receptor excision circle content of CD4+ T-cells, demonstrating a direct effect of IL-7 on thymic activity in this cohort.

T-cell regulation in rheumatoid arthritis.

Rheumatoid arthritis (RA) is characterized by a chronic T-cell response that has escaped normal control mechanisms. This review summarizes recent insights in pathways that are functional in RA and that favor continuous and pathogenic T-cell activation. T-cell activation is ultimately determined by positive signals from costimulatory molecules and negative signals from regulatory T cells. Blockade of the classic costimulatory pathway, CD28-CD80 or CD86, is beneficial in RA. Additional pathways that predominantly control the activation of memory and effector T cells are functionally important in synovial inflammation. Some of these costimulatory molecules (such as stimulatory killer cell immunoglobulin-like receptors and NKG2D) appear to be relatively specific for RA and not to play a role in normal immune responses. In addition to this predominance of positive signals, age-disproportionate decline in thymic activity in RA may lead to a diminution of regulatory T cells and loss of their negative signals. The successful treatment trial of RA with CTLA-4Ig clearly documents the importance of T-cell costimulation in RA disease activity. Novel costimulatory pathways may be of even greater significance than CD28 in RA and may represent promising new therapeutic targets. The finding of reduced thymic activity in RA is exciting and will stimulate further studies of T-cell homeostasis and the function of regulatory cells.

Evidence of thymic reconstitution after highly active antiretroviral therapy in HIV-1 infection.

We aimed to provide evidence of thymic reconstitution after highly active antiretroviral therapy (HAART) in HIV-1 infected patients and to correlate this with the restoration of peripheral naïve T cells. Positron emission tomography (PET) enables definitive evidence of thymic activity, indicating functional potential. In this case study, a single patient who initiated HAART demonstrated reconstitution of the naïve T-cell pool and underwent thymic PET scans at baseline and 2 and 6 months following initiation of therapy. Two patients who failed to demonstrate such reconstitution acted as controls. These patients (mean age 27 years) had chronic HIV infection with low CD4 T-cell counts (mean 82, range 9-160 cells/microL blood). Increased function of the thymus visualized by PET was correlated with phenotypic changes in CD4 and CD8 T cells in the periphery measured by flow cytometry, and with numbers of recent thymic emigrants measured by quantification of the numbers of T-cell receptor excision circles (TRECs) in peripheral cells. In one patient, clear correlations could be drawn between visible activity within the thymus, as measured by increased [F18]fluorodeoxyglucose (FDG) uptake, and regeneration of naïve CD4 (CD45RA/CD62L) T cells, increased numbers of CD4 T cells, controlled viraemia and increased numbers of recent thymic emigrants. A second patient displayed no increase in peripheral CD4 count and no increase in thymic activity. The third patient elected to stop therapy following the 2-month time point. The use of PET suggests that thymic activity may increase after HAART, indicating that the thymus has the potential to be functional even in HIV-1 infected persons with low CD4 T-cell counts.

Chemical analysis and antifungal activity of Thymus striatus.

The essential oil composition from Thymus striatus collected from Mountain Orjen (Montenegro) has been investigated by gas chromatography-mass spectrometry. Thymol, gamma-terpinene and p-cymene were found to be the major components. Furthermore, the oil and its major component, thymol, were analysed for potential antifungal activity against plant, animal and human pathogenic fungi from different genera by a macrodilution test. The oil exhibited a strong inhibitory effect against all fungi investigated.

Zinc modulates mRNA levels of cytokines.

Zinc plays an important role in cell-mediated immune function. Altered cellular immune response resulting from zinc deficiency leads to frequent microbial infections, thymic atrophy, decreased natural killer activity, decreased thymic hormone activity, and altered cytokine production. In this study, we examined the effect of zinc deficiency on IL-2 and IFN-gamma in HUT-78 (Th0) and D1.1 (Th1) cell lines and TNF-alpha, IL-1 beta, and IL-8 in the HL-60 (monocyte-macrophage) cell line. The results demonstrate that zinc deficiency decreased the levels of IL-2 and IFN-gamma cytokines and mRNAs in HUT-78 after 6 h of PMA/p-phytohemagglutinin (PHA) stimulation and in D1.1 cells after 6 h of PHA/ionomycin stimulation compared with the zinc-sufficient cells. However, zinc deficiency increased the levels of TNF-alpha, IL-1 beta, and IL-8 cytokines and mRNAs in HL-60 cells after 6 h of PMA stimulation compared with zinc-sufficient cells. Actinomycin D study suggests that the changes in the levels of these cytokine mRNAs were not the result of the stability affected by zinc but might be the result of altered expression of these cytokine genes. These data demonstrate that zinc mediates positively the gene expression of IL-2 and IFN-gamma in the Th1 cell line and negatively TNF-alpha, IL-1 beta, and IL-8 in the monocyte-macrophage cell line. Our study shows that the effect of zinc on gene expression and production of cytokines is cell lineage specific.